Revised classification of Acanthaceae and worldwide dichotomous keys

Abstract

Acanthaceae are among the most taxonomically diverse, geographically widespread, and morphologically and ecologically variable lineages of flowering plants. Most modern workers have estimated more than 4000 species and potentially more than 5000 species worldwide, thus placing Acanthaceae among the 12 or so most diverse families of angiosperms. This diversity is marked by exceptional morphological variation, particularly with respect to floral forms, growth forms, and pollen types. The present work represents a synthesis of knowledge generated over the past two decades on the taxonomy and systematics of this complex plant family. We place all 191 accepted genera within a revised classification of the family. Dichotomous keys (nine in total) to recognize the major lineages of Acanthaceae are presented together with geographically partitioned keys to all genera, covering (a) Africa, Madagascar, the Mediterranean region, and Arabia; (b) Asia and Australasia; and (c) the Americas. Finally, we validate several new tribes, subtribes, and genera, and provide new combinations for species where generic delimitation has changed. Our hope is that the present contribution serves to benefit future research on the systematics of Acanthaceae and provides a foundation upon which future classification efforts can be built.

Full text

Revised classification of Acanthaceae and worldwide
dichotomous keys
Erin A. Manzitto-Tripp,
1
*Iain Darbyshire,
2,3
*Thomas F. Daniel,
4
Carrie A. Kiel
5
& Lucinda A. McDade
5
1University of Colorado, Museum of Natural History and Department of Ecology and Evolutionary Biology, Boulder, Colorado 80309,
U.S.A.
2Royal Botanic Gardens, Kew, Herbarium, Richmond, Surrey, TW9 3AE, United Kingdom
3Honorary Research Associate, School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Johannesburg,
Private Bag 3, WITS 2050, South Africa
4California Academy of Sciences, Department of Botany, 55 Music Concourse Drive, Golden Gate Park, San Francisco, California
94118, U.S.A.
5California Botanic Garden, 1500 North College Avenue, Claremont, California 91711, U.S.A.
*Authors contributed equally to this manuscript
Address for correspondence: Erin A. Manzitto-Tripp, erin.manzittotripp@colorado.edu
DOI https://doi.org/10.1002/tax.12600
Abstract Acanthaceae are among the most taxonomically diverse, geographically widespread, and morphologically and ecologically
variable lineages of flowering plants. Most modern workers have estimated more than 4000 species and potentially more than 5000
species worldwide, thus placing Acanthaceae among the 12 or so most diverse families of angiosperms. This diversity is marked by
exceptional morphological variation, particularly with respect to floral forms, growth forms, and pollen types. The present work rep-
resents a synthesis of knowledge generated over the past two decades on the taxonomy and systematics of this complex plant family.
We place all 191 accepted genera within a revised classification of the family. Dichotomous keys (nine in total) to recognize the major
lineages of Acanthaceae are presented together with geographically partitioned keys to all genera, covering (a) Africa, Madagascar,
the Mediterranean region, and Arabia; (b) Asia and Australasia; and (c) the Americas. Finally, we validate several new tribes, sub-
tribes, and genera, and provide new combinations for species where generic delimitation has changed. Our hope is that the present
contribution serves to benefit future research on the systematics of Acanthaceae and provides a foundation upon which future classi-
fication efforts can be built.
Keywords circumscription; keys; molecular phylogeny; nomenclature; reclassification; taxonomy; worldwide
■INTRODUCTION
On a global scale, the Acanthaceae are a flowering plant
family of exceptional taxonomic diversity, morphological and
ecological variation, and geographical range (Figs. 1–3) (Dan-
iel, 1993; McDade & al., 2000a; Scotland & Vollesen, 2000;
Manktelow & al., 2001; Moylan & al., 2004; Wasshausen,
2006; Vollesen, 2008; Wood & Scotland, 2009; Tripp &
Darbyshire, 2017; Kiel & al., 2018; Darbyshire & al., 2020).
Estimates of the total number of species vary, but based on
checklists, regional treatments, and fieldwork that has recov-
ered many undescribed species, most modern workers have
predicted over 4000 species and potentially over 5000 spe-
cies. In this treatment, we estimate ~4900 species, placing
Acanthaceae among the 12 or so most diverse families of
flowering plants (McDade & al., 2008; Christenhusz & al.,
2017; POWO, 2020; Utteridge & Bramley, 2020). This diversity
is parsed among 191 genera recognized herein, with Justicia s.l.
(n ~ 1000, but non-monophyletic and inclusive of several other
genera), Ruellia (n ~ 350), Strobilanthes (n ~ 350), and Bar-
leria (n ~ 300) the most species-rich among these (Wood &
Scotland, 2009; Tripp & al., 2013a; Darbyshire & al., 2015,
2019a; Kiel & al., 2017, 2018; Tripp & Darbyshire, 2017).
Taxonomic diversity is concentrated in the Paleo- (Old
World, OW) and Neo- (New World, NW) tropics and subtro-
pics, but notable diversity occurs at temperate latitudes, parti-
cularly in Acanthus,Justicia,andRuellia (e.g., Daniel, 2015a).
Numerous centers of diversity exist worldwide, the most spe-
cies-rich among these being the tropical thornscrub, dry for-
ests, and savannas of Brazil and Mexico; the wet forests of
the Andean foothills in Bolivia, Peru, Ecuador, Colombia,
and Venezuela; the semi-deserts, savannas, dry forests and
submontane wet forests of tropical East and northeastern
Africa as well as central Africa; the wet and dry forests of
Madagascar; the Namib Desert and adjacent grasslands and
bushlands of Namibia and Angola; and varied ecosystems
Article history: Received: 3 Feb 2021 | returned for (first) revision: 29 Apr 2021 | (last) revision received: 14 Jul 2021 | accepted: 2 Aug 2021
Associate Editor: Dirk C. Albach | © 2021 The Authors.
TAXON published by John Wiley & Sons Ltd on behalf of International Association for Plant Taxonomy.
This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in
any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
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SYSTEMATICS AND PHYLOGENY

Fig. 1. Floral diversity among worldwide Acanthaceae. Collector, collection number, location of photograph, and photographer provided where
available. A,Dicliptera trifurca,Kiel & al. 122 (photo: C. Kiel), Costa Rica; B,Hypoestes phyllostachya,Kiel & Tripp 65 (photo: C. Kiel),
Mexico (native to Old World, widespread); C,Justicia refractifolia,Kiel & al. 137 (photo: C. Kiel), Costa Rica; D,Justicia costaricana, Kiel
& al. 81 (photo: C. Kiel), Costa Rica; E,Neuracanthus niveus, Not vouchered (photo: W. McCleland), Mali; F,Pachystachys spicata,Kiel & Velez
258 (photo: C. Kiel), Colombia; G,Tetramerium nervosum,Kiel & Tripp 75 (photo: C. Kiel), Mexico; H,Ruelliopsis setosa,Tripp & Dexter 799
(photo: E. Tripp), Namibia; I,Petalidium giessii,Tripp & Dexter 825 (photo: E. Tripp), Namibia; J,Blepharis pruinosa,Tripp & al. 884 (photo:
E. Tripp), Namibia; K,Acanthopsis hoffmanseggiana,Tripp & al. 2073 (photo: E. Tripp), Namibia; L,Aphelandra aurantiaca,Tripp & al. 5739,
Mexico; M,Acanthopale pubescens,Ballings & Wursten 1074 (photo: B. Wursten), Mozambique; N,Barleria oenotheroides,Tripp & al. 5755
(photo: E. Tripp), Mexico; O,Bravaisia integerrima,Tripp & Luján 519 (photo: E. Tripp), Venezuela; P,Brunoniella australis,Hosking 2952
(photo: J. Hosking), Australia; Q,Mendoncia aspera,Clarke & Tripp s.n. (photo: D. Clarke), Guyana; R,Dyschoriste repens,Tripp & Luján
516 (photo: E. Tripp), Venezuela; S,Barleria lancifolia,Tripp & Dexter 781 (photo: E. Tripp), Namibia; T,Louteridium donnellsmithii,Tripp
& Medina 9680 (photo: E. Tripp), Mexico; U,Calacanthus grandiflorus, Not vouchered (photo S. Yadav), India; V,Dinteracanthus asper,Tripp
& al. 2079 (photo: E. Tripp), Namibia; W,Anisosepalum alboviolaceum,Bytebier & al. 3279 (photo: Q. Luke), Dem. Repub. Congo; X,Ruellia
megasphaera,Tripp & al. 5756 (photo: E. Tripp), Mexico; Y,Odontonema glabrum,Tripp & al. 5763 (photo E. Tripp), Mexico; Z,Anisotes for-
mosissimus,Wursten 2020 (photo: B. Wursten), Mozambique; AA,Lepidagathis fischeri, Not vouchered (photo: I. Darbyshire), Tanzania; BB,
Asystasia malawiana,Mphamba 122 (photo: T. Harris), Mozambique.
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Fig. 2. Floral diversity among worldwide Acanthaceae. Collector, collection number, location of photograph, and photographer provided where
available. A,Andrographis echioides,Luke & Chidzinga 16414B (photo: Q. Luke), Kenya (naturalised, native to Asia); B,Cephalophis lukei,
Hyde 15.119.06 (photo: M. Hyde), Mozambique; C,Crabbea velutina,Ballings & Wursten 2391 (photo: B. Wursten), Zimbabwe; D,Crossandra
puberula,Wursten & al. 1946 (photo: B. Wursten), Mozambique; E,Duosperma crenatum, Not vouchered (photo: B. Wursten), Mozambique;
F,Champluviera populifolia,Cheek 7654 (photo: M. Cheek), Cameroon; G,Dyschoriste hildebrandtii,Wursten 951 (photo: B. Wursten),
Mozambique; H,Ecbolium tanzaniense,Suleiman & al. TTSA 235 (photo: I. Darbyshire), Tanzania; I,Elytraria acaulis, Not vouchered (photo:
B. Wursten), Mozambique; J,Isoglossa vulcanicola,Darbyshire & al. 1048 (photo: I. Darbyshire), Uganda; K,Justicia salviiflora,Tripp & al.
5773 (photo: E. Tripp), Mexico; L,Lankesteria elegans, Collector/photographer unknown, Cameroon; M,Lankesteria hispida,van der Burgt
1406 (photo: X. van der Burgt), Sierra Leone; N,Mackaya bella, Not vouchered (photo: I. Darbyshire), South Africa (cult.); O,Megalochlamys
hamata, Not vouchered (photo: B. Wursten), Zimbabwe; P,Mimulopsis excellens,Darbyshire & al. 1056 (photo: I. Darbyshire), Uganda; Q,Phy-
sacanthus batanganus,Cheek in Kami 4132 (photo: M. Cheek), Dem. Repub. Congo; R,Schaueriopsis variabilis,Luke 12527 (photo: Q. Luke),
Dem. Repub. Congo; S,Ruspolia seticalyx,Wursten 1859 (photo: B. Wursten), Mozambique; T,Thunbergia gregorii, Not vouchered (photo:
I. Darbyshire), Kenya; U,Whitfieldia orientalis,Suleiman & al. 5534 (photo: I. Darbyshire), Tanzania; V,Stenostephanus sessilifolius,Hammel
& al. 26074 (photo: C. Kiel), Costa Rica; W,Pseuderanthemum subviscosum, Not vouchered (photo: B. Wursten), Mozambique; X,Ruellia neesi-
ana,Tripp & Medina 5957 (photo: E. Tripp), Brazil; Y,Leandriella valvata,Thulin & Razafindraibe 11880 (photo: M. Thulin), Madagascar; Z,
Avicennia germinans,Daniel 11120 (photo: W. Eckerman), São Tomé; AA,Heteradelphia paulowilhelmia, Not vouchered (photo: T. Daniel),
São Tomé; BB,Lepidagathis grandidieri,Daniel & al. 11066 (photo: T. Daniel), Madagascar; CC,Chlamydacanthus euphorbioides,Daniel &
Ranarivelo 10584 (photo: T. Daniel), Madagascar.
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of tropical Asia, particularly in India (Daniel, 1993; Carine
& Scotland, 1998; Vollesen, 2008; Darbyshire & al., 2010,
2020; Kiel & al., 2017, 2018; Tripp & Darbyshire, 2017; Tripp
& al., 2017; Tripp & Luján, 2018; Madagascar Catalogue,
2020). Conversely, the family is noticeably absent or species-
poor in several regions at seemingly suitable latitudes inclu-
ding Australia, the Guiana Shield, and Mediterranean climate
zones worldwide. These patterns may in part be driven by
nutrient-poor edaphic conditions and/or climatic conditions
of these regions (e.g., winter rainfall, summer aridity). Centers
of endemism largely parallel centers of biodiversity world-
wide. Madagascar almost certainly hosts the highest degree
of endemism: of over 500 species of Acanthaceae, 93% are
considered to be endemic (Onjalalaina & Darbyshire, 2016;
Madagascar Catalogue, 2020). In addition to marked taxo-
nomic diversity worldwide, Acanthaceae have a notably rich
fossil record (Tripp & McDade, 2014).
As is frequently observed in tropical ecosystems charac-
terized by high alpha diversity, populations of species of
Acanthaceae tend to be small, with many consisting of one
Fig. 3. Examples of habitat diversity among worldwide Acanthaceae. Collector, collection number, location of photograph, and photographer pro-
vided where available. A,Petalidium crispum,Tripp & Dexter 4087 (photo: E. Tripp), Namibia; plants showing affinity for crevices of near-barren
schist rocks and associated slopes, near Van Zyl’s Pass; B,Avicennia marina, Not Vouchered (photo: I. Darbyshire), Tanzania; locally dominant in
intertidal mangrove communities near Lindi; note the presence of pneumatophores; C,Barleria aristata, Not Vouchered [but same location as Bid-
good & al. 5027] (photo: I. Darbyshire), Tanzania; locally common in dry Somalia-Masai woodland near the Lukosi River; D,Justicia fittonioides,
Suleiman & al. 5536 (photo: I. Darbyshire), Tanzania; abundant on the floor of seasonally dry coastal forest at Ruawa Forest Reserve near Lindi; E,
Ruelliopsis setosa,Tripp & Dexter 799 (photo: E. Tripp), Namibia; plants a dominant component of rocky savanna floor, acting as a “grass mimic”;
F,Blepharis ferox,Tripp & Dexter 4094 (photo: K. Dexter), Namibia; plants comprising one of the most abundant shrubs on barren sand of Namib
Desert, near Oropembe; G,Isoglossa dispersa, Not Vouchered (photo: P.K. Haba), Guinea; a mass-flowering plietesial species of moist lowland
and mid-elevation forest, here at Simandou; H,Justicia fittonioides,Suleiman & al. 5536 (photo: I. Darbyshire), Tanzania; showing the rosulate
habit of the plants in D; I,Pogonospermum salsola,Klaassen & al. 2537 (photo: E. Tripp), Namibia; plants represent the dominant shrubs on
the floor of the Namib Desert, which is typical of numerous species of this genus and of Petalidium,Blepharis, and Barleria in Namibia; J,Peta-
lidium welwitschii,Tripp & Dexter 4091 (photo: E. Tripp), Namibia; total dominance of Namib Desert near Hartmann’s Valley in the northwestern
Kaokoveld; K,Justicia americana,Daniel & Lott 10530 (photo: T. Daniel), U.S.A.; aquatic perennial herb at edge of Town Lake, Austin, Texas; L,
Lankesteria glandulosa Benoist, Daniel & al. 10453 (photo: T. Daniel), Madagascar; dying perennial herb along trail in seasonally moist forest,
Ankarana Special Reserve.
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to several (often fewer than 20) plants. This has long chal-
lenged tropical botanists in our attempt to understand the nat-
ural history of species in these regions. However, exceptions
exist: notable areas where species of Acanthaceae comprise
some of if not the most abundant and ecologically dominant
plants across the landscape (Fig. 3) include the Namib Desert
and surrounding drylands of Namibia and Angola (Tripp
& al., 2017; Darbyshire & al., 2019b, 2020), portions of
northeastern tropical Africa such as the Acacia-Commiphora
woodlands of southern Ethiopia and northern Kenya, and
monodominant stands of the Indian species Strobilanthes
kunthiana (Nees) T.Anderson ex Benth. and Barleria involu-
crata Nees in the Western Ghats (Annaselvam & Parthasara-
thy, 1999; Krishnan, 2000; Sharma & al., 2008). Although
perhaps best known in Strobilanthes (e.g., Bremekamp,
1944; Wood, 1994, 1999), synchronized mass-flowering of
perennially monocarpic (plietesial) Acanthaceae is a well-
documented phenomenon in a number of genera across sev-
eral clades (e.g., Thomas, 1996; Cheek & al., 2004; Daniel,
2006; Champluvier & Darbyshire, 2009; Darbyshire, 2009;
Champluvier & Fischer, 2020), with high ecological signifi-
cance. Other examples of monodominance in Acanthaceae
include species of Avicennia, which occur in extensive stands
of coastal mangrove communities worldwide (Tomlinson, 1986;
Beentje & Bandeira, 2007).
Species of Acanthaceae have long been appreciated for
their exceptional morphological diversity, particularly with re-
spect to floral forms, growth forms, and pollen types (Figs. 1,
2). Floral morphological diversity includes a broad spectrum of
colors ranging from red to purple, pink, yellow, orange, white,
green, and blue-green, and it is not atypical for sister species
to have strikingly divergent colors (e.g., Tripp & Manos, 2008;
Kiel & al., 2018). Diversity of floral forms among related spe-
cies is equally marked, with corolla morphology likely reflect-
ing adaptation to a variety of pollinators including bees, birds,
butterflies, hawkmoths, flies (especially bombyliids), and bats
(Grant, 1983; Hilsenbeck, 1983; Ramamoorthy, 1991; Daniel,
1993; Ezcurra, 1993; Vogel & al., 2004; Holmqvist & al.,
2005; Döll & al., 2007; Tripp & Manos, 2008; Heywood &
al., 2017; Tripp & Tsai, 2017; Kiel & al. in prep.).
Whereas most species of Acanthaceae are herbs or shrubs,
trees have evolved in parallel in several genera including
Aphelandra,Barleria,Justicia, and Louteridium. In particular,
species of Trichanthera and Bravaisia are nearly or fully arbo-
rescent (Daniel, 1988; Daniel & Véliz, 2009; Daniel, 2015b;
Darbyshire & Luke, 2016; Daniel & Tripp, 2018), as are mem-
bers of the mangrove genus Avicennia.
Species of Avicennia display adaptations to saline envi-
ronments, such as the presence of pneumatophores (Daniel,
2016). Elsewhere in the family, twining herbs and lianas are
frequent in subfamily Thunbergioideae (Borg & al., 2008).
Other unusual growth forms include that of African Dischisto-
calyx, which is reported to initiate developmentally as a terres-
trial herb before producing climbing shoots that anchor to tree
trunks or boulders and then produce epiphytic or lithophytic
flowering shoots (Cheek, 1995). This exceptional diversity across
growth forms, floral forms, and vegetative morphologies (Figs.
1–3) adds to the family’s intrigue for those who study it. However,
thismorphologicaldiversityisalsofrustratingowingtoclearly
homoplasious patterns of evolution that have resulted in the pre-
sence of similar features in only distantly related lineages. This
evolutionary vagility has long plagued efforts to interpret tax-
onomy, morphological diversity, and evolution (Moylan & al.,
2004; Tripp, 2007; Daniel & al., 2008; Tripp & Manos, 2008;
Wood & Scotland, 2009; Kiel & al., 2017, 2018; McDade &
al., 2018; Darbyshire & al., 2019a).
Since the 19th century, there has been only one reclassifi-
cation of the family. Scotland & Vollesen (2000) treated a total
of 221 genera, parsed among three subfamilies, two tribes, and
four subtribes, with 20 genera remaining unplaced. Their
study was made possible largely through comparative morpho-
logical (including palynological) interpretation of variation in
the family, together with a limited number of early, molecular
phylogenetic studies. Since this landmark recircumscription,
extensive new knowledge, especially molecular data placed in
a phylogenetic context, has accumulated (e.g., Manktelow &
al., 2001; Schwarzbach & McDade, 2002; Moylan & al.,
2004; McDade & al., 2005, 2008, 2012, 2018; Schmidt-
Lebuhn & al., 2005; Kiel & al., 2006, 2017, 2018; Tripp,
2007; Wortley & al., 2007; Borg & al., 2008; Daniel & al.,
2008; Tripp & al., 2013a,b; Kiel & McDade, 2014; Fisher &
al., 2015; Deng & al., 2016; Tripp & Darbyshire, 2017; Darby-
shire & al., 2019a,b). Cumulatively, these and other works have
placed nearly all of the 20 genera that were unclassified in
Scotland & Vollesen (2000), as well as provided evidence that
several genera should be transferred to other tribes or sub-
tribes (e.g., Manktelow & al., 2001; McDade & al., 2008; Tripp
& al., 2013a).
Despite the high species richness and a nearly worldwide
distribution, surprisingly few professional botanists are actively
pursuing and publishing new phylogenetic and taxonomic
knowledge in Acanthaceae. Tripp & Darbyshire (2017) la-
mented this low “scholars to species”ratio and estimated fewer
than 20 such individuals worldwide, of whom ~12 are pro-
viding regular contributions. This disparity contributed to the
placement of Acanthaceae among the worst offenders in an
angiosperm-wide synthesis of remaining knowledge gaps, thus
challenging full achievement of “Targets”put forward in the
Global Strategy for Plant Conservation (Paton & al., 2008).
Tripp & Darbyshire (2017) further commented that phyloge-
netic studies centered around the generation and analysis of
new molecular data yield results more quickly, are published
in journals with higher impact factors, and have higher cita-
tion rates than are taxonomic studies that attempt to translate
information coming out of such molecular studies into up-
dated treatments and classifications. Many taxonomic papers
are slower to produce, compiled by fewer specialists, and are
published in journals with lower impact factors. Scientists are
more commonly rewarded for publishing papers in high im-
pact factor journals with high citation rates and may thus find
it challenging to devote research time to taxonomic work, hin-
dering taxonomic progress. That said, the years since Scotland
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&Vollesen’s (2000) classification have witnessed major strides
in our understanding of species diversity in Acanthaceae in
many parts of the world, from monographic and floristic perspec-
tives in addition to the aforementioned phylogenetic advances.
Progress has been most notable in Africa (e.g., Balkwill & Wel-
man, 2000; Darbyshire & Harris, 2006; Ensermu, 2006; Hedrén
& Thulin, 2006; Vollesen, 2006, 2007, 2008, 2013; Darbyshire
& Vollesen, 2007; Champluvier & Darbyshire, 2009, 2012;
Daniel & Figueiredo, 2009; Darbyshire, 2009; Darbyshire &
al., 2009, 2010, 2011, 2019c; Balkwill & al., 2017; Magnaghi
& Daniel, 2017; Breteler & Wieringa, 2018; Steyn, 2018), the
Americas (e.g., Durkee, 2001; Ezcurra, 2002, 2018; Daniel &
Acosta, 2003; Daniel, 2004, 2005, 2010, 2015b, 2016; Wass-
hausen & Wood, 2004; McDade & Tripp, 2007; Kameyama,
2008; Indriunas, 2011; Wasshausen, 2013; Franck & Daniel,
2015; Côrtes & al., 2016a; Braz & Monteiro, 2017; Da Silva
Monteiro & al., 2018; Daniel & Tripp, 2018; Tripp & Luján,
2018; Da Costa-Lima & de Oliveira Chagas, 2019; McDade
& al., 2019; Zanatta, 2019; Burgos-Hernández & Castillo-
Campos, 2020; McDade, 2020; Braz & al., 2021) and, to a
lesser extent, in tropical Asia (e.g., Moylan & al., 2002; Wood
& al., 2003; Carine & al., 2004; Deng & al., 2006; Wood &
Scotland, 2009; Shendage & Yadav, 2010; Hu & al., 2011;
Wood, 2014; Gnanasekaran & al., 2016; Bongcheewin & al.,
2019; Deng, 2019; Rueangsawang & al., 2020), as well as in
groups that are wide-ranging (e.g., Vollesen, 2000; Daniel &
McDade, 2014). These works have, in turn, increased the
knowledge base for classification of this diverse and complex
family.
The present reclassification of Acanthaceae represents
our synthesis of information from the last two decades of phy-
logenetic, floristic, taxonomic, and nomenclatural research in
the family. For the first time since Lindau (1895), dichoto-
mous keys to the major lineages and genera of Acanthaceae
are presented, along with geographically structured keys. We
discuss previously unplaced as well as newly placed genera.
We furthermore take a first pass at delimiting the geograph-
ical distributions of all recognized genera within the family.
We validate a number of names and make several new combi-
nations of names where required. Specifically, our contribu-
tion includes the following sections, in addition to the pri-
mary text:
I. The classif ication
II. Keys to the subfamilies, tribes, and genera of Acanthaceae
III. Geographical keys to the genera of Acanthaceae
IV. Validation of names (tribes, subtribes, genera)
V. New synonymies and combinations (species)
Our revised classification reflects a f irst pass at interpret-
ing and reinterpreting morphological variation in light of mo-
lecular results based largely on Sanger sequence data. With
anticipation and optimism, we expect that subsequent revi-
sions will emphasize results from next-generation sequencing
methods and will incorporate results for previously unsampled
or poorly sampled lineages. Phylogenomic analyses primarily
emphasizing RADseq datasets for Acanthaceae are growing
rapidly and already include Petalidium (Tripp & al., 2017),
Ruellieae (Tripp & Darbyshire, 2020), Ruellia (Tripp & Daniel,
in prep.), Louteridium (Daniel & Tripp, 2018), Barleria (Co-
mito, 2019; Comito & al., in rev.), Justicia (Kiel & al., in prep.),
and Monechma (Darbyshire & al., 2020). The present contri-
bution builds upon the foundation laid by Scotland & Vollesen
(2000) to produce a revised classification, which future phy-
logenetic, taxonomic, and floristic contributions can further
refine.
■METHODS
To facilitate reclassification of Acanthaceae, we surveyed
(1) historical literature (i.e., prior to the rise of molecular phylo-
genetics) followed by (2) more recent studies, primarily but not
entirely those utilizing molecular phylogenetic analyses of rela-
tionships among various lineages of Acanthaceae. We sought
to include studies of lineages that have been treated among
other plant families at various times in the past (e.g., Avicennia,
Mendoncia,Thunbergia). A list of accepted genera was pre-
pared based on the cumulative opinions of the authors, in-
formed by numerous published contributions. Thorough histo-
ries of taxonomic accounts of Acanthaceae (e.g., Bentham &
Hooker, 1876) have been provided in numerous prior works
and it is not our intention to repeat these accounts here. Like-
wise, many of the phylogenetic, monographic, and floristic
works cited in the Introduction provided extensive evidence of
morphological synapomorphies and other suites of traits that
were used to inform the taxonomic classification presented
herein. Evolution of these traits is not discussed in detail in
the current work but can be found in these primary references.
Keys to subfamilies, tribes, and genera of Acanthaceae on
a worldwide basis (except for Justicieae) and keys to all genera
based on major geographical regions were prepared. We re-
frained from preparing a key to Justicieae because the tribe in-
cludes numerous poorly known genera as well as genera that
are inadequately circumscribed and differentiated at present.
Following Part I (The classification), twelve dichotomous keys
are presented here: Part II contains nine keys, these to the sub-
families, tribes, and genera; Part III contains three keys, these
geographically organized. The keys were constructed through
a combination of extensive reviewof available literature (partic-
ularly monographs and floristic accounts) and study of herbar-
ium material housed at a wide range of herbaria and botanical
gardens, but with most extensive reference to the collections
at B, BM, BR, C, CAS, COLO, EA, G, K, L, LISC, MEXU,
MO, NY, P, RSA, S, US and WAG. Many images of type
specimens were accessed via JSTOR Global Plants (https://
plants.jstor.org/).
In citing type material, an exclamation mark (!) is used
whenever direct study of specimens was undertaken. An aster-
isk (*) indicates that study was limited to online images of
specimens. Numbers associated with type specimens refer to
specimen barcodes.
Pollen terminology largely follows Walker & Doyle (1975),
supplemented by Hesse & al. (2009).
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■RESULTS
The present classification of Acanthaceae (Fig. 4) includes
four subfamilies: Nelsonioideae, Avicennioideae, Thunber-
gioideae, and Acanthoideae. In prior works (e.g., McDade &
al., 2008), these have together been referred to as Acanthaceae
sensu lato (s.l.). Thunbergioideae are divided into two tribes:
Mendoncieae and Thunbergieae. Within Acanthoideae, which
encompass by far the greatest taxonomic diversity, eight tribes
are recognized: Acantheae, Physacantheae, Barlerieae, Andro-
graphideae, Whitfieldieae, Neuracantheae, Ruellieae, and
Justicieae. Within these tribes, a total of 19 subtribes are recog-
nized: Acanthinae and Aphelandrinae (Acantheae); Lankes-
teriinae and Whitfieldiinae (Whitfieldieae); Dinteracanthinae,
Erantheminae, Hygrophilinae, Mcdadeinae, Mimulopsidinae,
Petalidiinae, Phaulopsidinae, Ruelliinae, Strobilanthinae, and
Trichantherinae (Ruellieae); and Graptophyllinae, Isoglossi-
nae, Justiciinae, Monotheciinae, and Tetrameriinae (Justicieae).
In total, 191 genera are recognized in this treatment. Of
these, all are placed taxonomically except three members of
Ruellieae (Diceratotheca,Stenothyrsus,Xylacanthus), five of
Justicieae (Dolichostachys,Ichthyostoma,Samuelssonia,Stre-
blacanthus,Tessmanniacanthus), and one genus that is cur-
rently treated as Acanthaceae Incertae Sedis (Ritonia). Four
genera are excluded from the classification for varied reasons,
as described below: Gymnophragma,Schwabea,Sericospora,
and Strobilacanthus. Two genera from Madagascar that have
been referred to widely in the literature but had not been
validly published are validated below: Dolichostachys and
Va v a ra . Finally, updated generic placements and new combi-
nations are made for numerous species.
The present classification differs from that of Scotland &
Vollesen (2000) in several ways. Their subtribes Andrographi-
nae (= Andrographidinae), Barleriinae, Ruelliinae, and Justi-
ciinae have here been elevated to tribal rank within subfamily
Acanthoideae. Further, we recognize three additional tribes
Mendoncieae
NELSONIOIDIEAE
Justiciinae
Physacantheae
Monotheciinae
Neuracantheae
Thunbergieae
Acanthinae
Isoglossinae
AVICENNIOIDEAE
Aphelandrinae
Barlerieae
Andrographideae
Whitfieldiinae
Lankesteriinae
Tetrameriinae
Graptophyllinae
Petalidiinae
Hygrophilinae
Mimulopsidinae
Erantheminae
Physacantheae
Trichantherinae
Ruelliinae
Mcdadeinae
Dinteracanthinae
Strobilanthinae
Phaulopsidinae
THUNBERGIOIDEAE
Acantheae
Whitfieldieae
Justicieae
Ruellieae
ACANTHOIDEAE
*
*
Fig. 4. Schematic molecular phylogeny of the Acanthaceae, which serves as the foundation for the present reclassification. Phylogeny represents
current understanding of evolutionary relationships among major lineages of Acanthaceae based on numerous phylogenetic works, as cited
throughout this study. Depicted are the 4 subfamilies (capital letters), 10 tribes (bold), and 19 subtribes (not in bold, not in caps) recognized in
the present study. Key diagnostic morphological characters for the subfamilies and tribes are provided in Table 1 and Fig. 5. Asterisks and dashed
lines indicate uncertain phylogenetic placement of Physacantheae, either within or sister to Ruellieae or Acantheae (see text).
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within that subfamily for genera that were either unplaced or
(in the case of Physacanthus) misplaced in the earlier classifi-
cation: Neuracantheae, Physacantheae, and Whitfieldieae. In
addition, we here subdivide Thunbergioideae into two tribes
and recognize 15 subtribes across Justicieae and Ruellieae.
Nineteen of the 20 unplaced genera listed by Scotland & Vol-
lesen (2000) have been placed either as accepted genera within
the present classification (13 genera) or in synonymy (6 gen-
era). The remaining taxon, “Idiacanthus Leonard”, was never
validly published and thus was a nomen nudum when in-
cluded by Scotland & Vollesen (2000). We have also revised
the placement of a number of genera and placed into syno-
nymy a number of other genera recognized by these authors
(Appendix 1).
In Appendix 2, we propose a numeric linear sequence for
the 191 accepted genera, informed by phylogenetic and mor-
phological evidence accumulated to date. This is aimed to-
wards assisting curation of herbarium collections of Acantha-
ceae in herbaria that opt for a systematic rather than alpha-
betic sequence.
■DISCUSSION
Acanthaceae s.l.: one family or four? —The delimita-
tion of Acanthaceae has varied considerably over time and
continues to be contentious. Lindau (1895), in his major
classification of the family, recognized a broadly circumscri-
bed Acanthaceae comprising four subfamilies: Acanthoideae,
Nelsonioideae, Thunbergioideae and Mendoncioideae. Breme-
kamp’s later (1965) reclassification excluded groups that lack
retinaculate fruits and therefore he recognized Thunbergioi-
deae and Mendoncioideae as separate families (Thunbergia-
ceae and Mendonciaceae) and transferred Nelsonioideae to
Scrophulariaceae. The recent body of systematic studies in
Acanthaceae has demonstrated a close relationship between
thunbergioids and mendoncioids (Schönenberger & Endress,
1998; Borg & al., 2008) and also shown that nelsonioids are
sister to other Acanthaceae and are not closely related to
any of the former members of Scrophulariaceae (Hedrén &
al., 1995; McDade & al., 2012). In the most recent classifica-
tion of the Acanthaceae prior to the present work, drawing
on available molecular and morphological data, Scotland &
Vollesen (2000) adopted a similar delimitation to that of
Lindau (1895) and included the clades with non-retinaculate
fruits within Acanthaceae. Scotland & Vollesen (2000) re-
cognized three subfamilies (Nelsonioideae, Thunbergioideae,
Acanthoideae), with mendoncioids being included within Thun-
bergioideae. More recently, molecular phylogenetic studies
have demonstrated that the woody mangrove genus Avicen-
nia is nested within Acanthaceae s.l., sister to Thunbergio-
ideae (Schwarzbach & McDade, 2002). This genus was pre-
viously treated either within its own family, Avicenniaceae
(e.g., Fernandes, 2005; Brummitt, 2007) or within the Verbe-
naceae (e.g., Verdcourt, 1992). Results presented in Schwarz-
bach & McDade (2002), although surprising in view of
the morphological differences between Avicennia and other
Acanthaceae, have been supported consistently by subsequent
molecular analyses (e.g., Borg & al., 2008; McDade & al.,
2008), and the genus is now widely accepted as belonging to
Acanthaceae (Angiosperm Phylogeny Group, 2016), as treated
herein.
All major studies on the Lamiales have demonstrated that
Acanthaceae, including Avicennia, are monophyletic (McDade
& al., 2008, 2012; Schäferhoff & al., 2010). McDade & al.
(2012) hypothesized that indurate, explosively dehiscent
capsules are synapomorphic for Acanthaceae, albeit with
autapomorphic leathery, non-explosively dehiscent capsules
in Avicennia and drupaceous fruits in Mendoncia and Anoma-
canthus. This combined molecular and morphological evi-
dence supports recognition of a single family and, indeed, most
modern floristic and phylogenetic treatments of Acanthaceae,
prior and subsequent to McDade & al. (2012), follow this broad
circumscription (e.g., Scotland & Vollesen, 2000; Ensermu,
2006; McDade & al., 2008; Vollesen, 2008, 2013; Darby-
shire & al., 2010, 2015), with a few others (e.g., Cronquist,
1981) taking alternative stances.
Nevertheless, under this broad circumscription, it is diffi-
cult to diagnose Acanthaceae in relation to a number of the
other ~24 families that comprise Lamiales (Stevens, 2001–).
This is due in part to the broad range of morphological varia-
tion that Acanthaceae encompass and begs the question as to
whether a narrower family definition might benefit classifi-
cation efforts within Lamiales through improved diagnosis
of segregate families based on morphological traits. Following
Bremekamp’s (1965) narrower circumscription, Acanthaceae
sensu stricto (s.str.; i.e., here, Acanthoideae), is by far the most
species-rich clade within Acanthaceae, containing approxi-
mately 90% of the total number of taxa. This clade is easily
characterized by the synapomorphy of presence of retinacula
(i.e., modified hook-shaped funiculi) contained within explo-
sivelydehiscent capsules. There are very few instances of auta-
pomorphic, evolutionary diversions from this morphology
(e.g., capsules of a few Justicieae: Aphanosperma,Chalaro-
thyrsus, and a few Justicia species [Kiel & al., 2017] have
poorly developed or not clearly discernible retinacula). Reti-
nacula are absent in the remaining subfamilies of Acanthaceae
s.l. (but see fig. 9E in Daniel & McDade, 2014 for images
of structures in some Nelsonioideae that may represent early
stages in the evolution of retinacula). Indeed, among angio-
sperms, retinacula were thought to be unique to Acanthaceae
s.str., except that they are also present in Thomandersia, a ge-
nus previously treated within Acanthaceae but subsequently
found to be more distantly related (Wortley & al., 2007;
McDade & al., 2012). Thomandersia is thus now treated
within its own monogeneric family, Thomandersiaceae; plants
of Thomandersia differ from Acanthaceae s.str. in lacking ex-
plosively dehiscent capsules as well as lacking articulation of
the stems (Wortley & al., 2007).
The other major lineages of Acanthaceae s.l. (i.e., Nel-
sonioideae, Thunbergioideae, and the genus Avicennia) are
also well delimited based on morphological traits, although
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morphological synapomorphies have not been determined
for all of them. These lineages can be differentiated readily from
one another (see key to subfamilies below) and from other fami-
lies of Lamiales, although the separation of Nelsonioideae from
some of the segregate families in the former Scrophulariaceae
remains challenging on morphological grounds.
Given the stipulations and exceptions noted above, we
here adopt a compromise classification in which we recognize
Acanthaceae s.l., which are united by explosively dehiscent
capsules, with the exception of the autapomorphic fruit types
noted above. We recognize four morphologically distinct
clades as separate subfamilies: Nelsonioideae, Avicennioideae,
Thunbergioideae, and Acanthoideae. This revised family clas-
sification was adopted in Stevens (2001–)aswellasbythe
Angiosperm Phylogeny Group (2016) and is similar to that pro-
posed by Reveal (2012).
An overview of the subfamilies, tribes, and subtribes of
Acanthaceae. —Below, we provide abridged descriptions of
the four subfamilies and their tribes and subtribes, as a general
overview of the phylogeny and upper-level classification of
the family (Fig. 4). We caution that several genera of Acantha-
ceae have yet to be included in phylogenetic analyses such that
this synopsis remains a working hypothesis pending further
phylogenetic studies. Key diagnostic morphological charac-
ters for the subfamilies and tribes are provided in Table 1
and are discussed below.
Nelsonioideae. —This subfamily of mostly herbaceous
and subshrubby species (ca. 175 spp.) is united by the follow-
ing morphological characters: descending-cochlear corolla
aestivation (unique in Acanthaceae and proposed as a prob-
able synapomorphy by Daniel & McDade, 2014) (Fig. 5D),
presence of persistent endosperm in the seeds (versus usually
exalbuminous seeds elsewhere in Acanthaceae, although the
trait has yet to be thoroughly studied across the family and ex-
ceptions have been noted, e.g., Mohan Ram & Wadhi, 1964),
absence of cystoliths and retinacula (both features shared with
Thunbergioideae and Avicennioideae), capsules with 6–68
seeds (which separates this group from other non-retinaculate
Acanthaceae, where fruits have 1–4 seeds) and, in many spe-
cies, spirally arranged flowers in the inflorescence (versus op-
posite or secund in other Acanthaceae). Thus, Nelsonioideae
are relatively easy to separate from other Acanthaceae. Explo-
sive capsule dehiscence and the presence of papilliform and/or
elongate (but not indurate) modified funiculi are likely to be
diagnostic, but this requires further investigation. The generic
delimitation and diversity were considered globally by Daniel
& McDade (2014; see also Braz & al., 2021). Six genera are
currently recognized, and the subfamily is pantropical.
Avicennioideae. —This pantropical subfamily of ca. 8 spe-
cies comprises the mangrove tree and shrub genus Avicennia.
Unique in Acanthaceae, plants of Avicennia display adaptations
to saltwater inundation, including the presence of pneumato-
phores (Tomlinson, 1986; Verdcourt, 1992; Daniel, 2016).
Plants lack cystoliths and have only tardily dehiscent, leathery
fruits bearing a single seed (Mendoncia and Anomacanthus in
Thunbergioideae have indehiscent drupaceous fruits). Floral
morphology is variable: the A. marina group is unusual in hav-
ing actinomorphic, 4-lobed corollas (number of corolla lobes =
number of stamens) with valvate aestivation (Tomlinson, 1986)
(Fig. 5E), the only known occurrence of this aestivation pattern
in Acanthaceae. However, other species of Avicennia have zygo-
morphic corollas with left-contort aestivation (Tomlinson,
1986; Borg & Schönenberger, 2011) (Fig. 5A). The genus is
composed of two monophyletic lineages: one of Atlantic-East
Pacific taxa and a second of Indo-West Pacific taxa (Li & al.,
2016). A recent study of Avicennia (Cornejo, 2020) proposed
subdivision of the genus into two distinct genera, Avicen nia
and Hilairanthus, on the basis of monophyletic units in combi-
nation with morphological distinctiveness. However, the degree
of morphological variation between these two lineages is com-
parable to variation among lineages within many other genera
of Acanthaceae, e.g., Ruellia and Barleria. Moreover, there is
comparable variation within the lineage that includes the type
alone, Avicennia marina. As such, we recognize Avicennia as
broadly circumscribed, especially given the numerous synapo-
morphies for the genus, as described above.
Thunbergioideae. —With ca. 260 species in five genera,
plants of this pantropical and subtropical subfamily are primar-
ily vines and lianas that climb by twining (Borg & al., 2008),
although a significant number of species of Thunbergia are
perennial herbs or shrubs, presumably secondarily. Clambering
and vine-like plants are sometimes encountered elsewhere in
the family, but twining climbers appear to be known only in,
and synapomorphic for, Thunbergioideae. Other distinguish-
ing characters (and probable synapomorphies) common to all
genera in Thunbergioideae include an involucre or epicalyx of
paired, large, spathaceous bracteoles subtending each flower, a
highly reduced and modified calyx, and anthers that dehisce
by pores or short, slit-like openings. In their study of floral devel-
opment in Mendoncia,Pseudocalyx,andThunbergia, Schönen-
berger & Endress (1998) demonstrated that these genera share
similar types of inflorescences and features of the anther thecae.
Several unusual types of pollen occur among, and are synapo-
morphic for, genera of Thunbergioideae. The two tribes (Men-
doncieae, Thunbergieae) are readily distinguishable by their
fruits: fleshy and indehiscent (drupaceous) in Mendoncieae vs.
woody and explosively dehiscent (capsular) in Thunbergieae.
Like those in Nelsonioideae and Avicennioideae, plants of
this subfamily lack cystoliths and retinacula. Based on phyloge-
netic studies to date, Pseudocalyx is sister to Thunbergia, and both
of these genera together are sister to Mendoncia (Borg & al.,
2008). Meyenia and Anomacanthus have yet to be included in a
phylogenetic analysis. Among the five genera, only Mendon-
cia occurs natively in the NW, where it has undergone ex-
tensive speciation.
Thunbergieae. –This tribe consists of ca. 160 species
treated currently among three genera (Meyenia,Pseudocalyx,
Thunbergia) native to the Paleotropics and subtropics. Plants
share numerous characteristics, including ovoid and promi-
nently beaked capsules with the seeds borne in a subglobose
to 4-partite capsular base, up to four seeds, and anther thecae
showing considerable diversity in pubescence and appendages.
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Table 1. Key morphological characters for the major lineages of Acanthaceae. Table includes some exceptions to general trends within a given
lineage but is not comprehensive in terms of all exceptions that exist.
Character Nelsonioideae Avicennioideae Thunbergioideae Acantheae Physacantheae Andrographideae
Cystoliths Absent Absent Absent Absent Absent Present
Corolla
aestivation
Descending-
cochlear
Left-contort,
slightly
imbricate,
or valvate
Left-contort;
rarely ascending-
cochlear
Ascending-
cochlear or
“open”
Left-contort Ascending-
cochlear
No. of fertile
stamens
2or4 4 4 4 4 2
No. of anther
thecae per
fertile stamen
2221 12
Pollen
characteristics
3-colpate to
3-colporate,
pseudocolpi
absent
3-colporate,
pseudocolpi
absent
Spiraperturate,
3–6-colpate, or
7–9-lobate
and -colpate,
pseudocolpi
absent
Usually 3-colpate,
sometimes with
numerous short
colpus-like aper-
tures dividing grains
into polygonal re-
gions, rarely with
pseudocolpi
3-colporate,
9-pseudocolpate
3-colporate,
3-pororate,
ectoapertural
membrane and/or
thickened margin
often with spines,
pseudocolpi absent
Fruit
characteristics
Mostly small
capsules varying
from thin- to thick-
walled, sometimes
rostrate
Leathery to fleshy
capsule that is
non-explosive,
and tardily
dehiscent
Large woody
rostrate capsule;
OR globose or
ellipsoid drupe
Fusiform or
shortly rostrate
capsule
Linear capsule Linear and
4-angular or
compressed elliptic,
oblanceolate or
narrowly oblong
capsule
Hooked
retinacula
Absent Absent Absent Present Present Present
No. of
ovules*
8 to many 4 1, 2 or 4 4 6–10 4 to many
No. of seeds*8–30 (–68) 1 1, 2 or 4 2–4(4
–)6–10 4 to many
Seed
sculpture /
trichomes
Variably smooth,
pitted, with minute
protrusions and
with or without
hygroscopic
trichomes (these
simple or branched)
Smooth Smooth or
sculptured, with a
prominent scar or
hole on one side
(in drupaceous
genera, a woody
stone)
Dense hygro-
scopic trichomes,
dense scales or
tuberculate, glan-
dular puberulous,
smooth or glabrous,
or otherwise variable
With pale
straight or
flexuose
papillae-like
trichomes
With or without
dense hygroscopic
trichomes or non-
hygroscopic
trichomes, smooth
or sculptured
Other
diagnostic or
informative
characters
Flowers often
alternate to spirally
arranged on
inflorescence,
although can be
opposite
Mangrove shrubs
or trees with
pneumatophores,
and plants
cryptoviviparous
Often twiners;
flowers subtended
by paired clasping
bracteoles
Leaves often
variegated;
long-cylindric
or inflated calyx
with short lobes
*Acanthaceae specialists have, in the past, described either the numbers of ovules or the numbers of seeds for a given taxon. We here provide
ranges for both the numbers of ovules (i.e., total number, regardless of whether fertilized and later developing into a seed) as well as the
number of seeds (i.e., the total number of ovules that were fertilized and later developed to maturity). We note that, for the vast majority of
taxa, we are uncertain as to what minimum seed set is required for capsule development to maturation.
^Pollen of Borneacanthus and Pseudodicliptera are not well known.
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Barlerieae Neuracantheae Whitfieldieae Ruellieae Justicieae Character
Present Present Present Present Present Cystoliths
Quincuncial Induplicate Left-contort Left-contort Ascending-cochlear Corolla
aestivation
2or4 4 2(Lankesteria) or 4 2 or 4 2 or 4 No. of fertile
stamens
2, or mixed
2×2-thecous and
2×1-thecous
Mixed
2×2-thecous
and
2×1-thecous
2 2 1 or 2; if 4 stamens
then 2-thecous or
mixed 2×2-thecous,
2×1-thecous
No. of anther
thecae per
fertile stamen
Mostly 3-colporate
or 3-porate, inter-
apertural exine often
coarsely reticulate,
pseudocolpi absent^
3-colporate,
interapertural
exine finely
perforate,
pseudocolpi
absent
Usually lenticular,
2-pororate with
ectoaperture
usually very large,
sometimes
3-pororate
or spherical and
pantoforate,
pseudocolpi absent
Diverse; germinal
apertures 2 to many,
porate to colporate
or pantoforate; tectum
often raised flanking
apertures, pseudocolpi
often present and
usually more than 2
between germinal
apertures
Diverse, germinal
apertures 2–6,
(porate to) pororate
to colporate,
pseudocolpi often
present but rarely
(if ever) more than
2 between germinal
apertures
Pollen
characteristics
Fusiform or
rostrate capsule,
rarely stipitate
Fusiform
or rostrate
capsule
Stipitate or fusiform
capsule
Stipitate, linear or
fusiform capsule
Stipitate, sometimes
also shortly rostrate
capsule
Fruit
characteristics
Present Present Present Present Present Hooked
retinacula
4 2 or 4 2 or 4 2–32 2 or 4 No. of
ovules*
2–42–42–42–28 2–4 No. of seeds*
Dense hygroscopic
trichomes or fine
?non-hygroscopic
trichomes, rarely
glabrous and smooth
Dense
hygroscopic
trichomes
Raised concentric
rings at least towards
the rim; glabrous
or (Lankesteria)
with hygroscopic
trichomes
Dense hygroscopic
trichomes or these
restricted to the rim,
rarely absent
Smooth or often
sculptured
(tubercles, spines,
verrucae, etc.),
and/or with
hygroscopic or
non-hygroscopic
trichomes
Seed
sculpture /
trichomes
Cystoliths can
occur in adjoining
cells
Calyx
bilabiate
(anterior lip
2-notched,
posterior lip
3-notched)
Inflorescence units
often subtended by
conspicuous paired
clasping bracteoles
Filament curtain
usually present, and
thecae sometimes with
basal appendages
Anther thecae
sometimes offset to
superposed and/or
oblique, and one
or both thecae
sometimes with
basal appendages
Other
diagnostic or
informative
characters
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These plants differ conspicuously from other Acanthaceae by
the spiraperturate pollen of Pseudocalyx and Thunbergia,and
the 7–9-lobate and -colpate pollen of Meyenia (Bremekamp,
1942).
Mendoncieae. –Two genera (Anomacanthus,Mendon-
cia) are currently treated in this tribe of ca. 100 spp., which
occurs in Africa, Madagascar/Mayotte, and the Neotropics.
They share the synapomorphy of drupaceous fruits, these most
frequently with a single, large seed (perhaps the largest in the
family); drupes of Anomacanthus are 2-seeded. Schönenberger
& Endress (1998) confirmed that, like many other members of
the family, the ovary of Mendoncia is composed initially of two
locules containing four ovules; however, later in development
abortion yields a single locule with two fertile ovules, only one
of which normally develops into a seed.
Acanthoideae. —Acanthoideae, consisting of ca. 4450
species, comprise by far the greatest morphological diversity
and species richness within Acanthaceae. This lineage is read-
ily delimited morphologically by the presence of capsules
with retinacula. The global “success”of this group in terms of
overall species richness may be explained in part by the evolu-
tionary innovation of retinacula. It has been demonstrated re-
cently that retinacula facilitate efficient launching and backspin
of seeds of Acanthaceae at the fastest rate documented to date
in nature (Cooper & al., 2018). We speculate that this capacity
to launch seeds distant from source parent plants both minimizes
intraspecific competition (Janzen, 1970; Connell, 1971) and aids
in the establishment of populations in new niches. The follow-
ing eight tribes are, for the most part, clearly delimited, but at
times delimitation requires evidence from multiple characters,
as well as study of both microscopic and macroscopic features.
Acantheae. –Acantheae, with some ca. 550 species, are
well-delimited morphologically: they are the only clade to
combine retinaculate capsules with absence of cystoliths and
presence of four monothecous stamens (the monogeneric tribe
Physacantheae is the exception, see below). In addition, pollen
of members of Acantheae are colpate and lack endoapertures,
which are present in almost all other Acanthoideae. Acantheae
can be further divided into two lineages: Aphelandrinae con-
sist of species with bilabiate or subrotate corollas that occur
primarily in the Neotropics but with representation in the Paleo-
tropics (Stenandriopsis), and Acanthinae, which are restricted
to the Paleotropics and have flowers with all five corolla lobes
directed ventrally (McDade & al., 2005).
Physacantheae. –Physacantheae, with three species
currently recognized, comprise the single continental African
forest genus Physacanthus. Tripp & al. (2013b) hypothesized
an ancient origin of “wide hybridization”between members
of Acantheae and Ruellieae for Physacanthus, and presented
molecular and morphological evidence that supported this
hypothesis. Physacanthus shares with Acantheae four mono-
thecous stamens and absence of cystoliths but shares with
Ruellieae colporate pollen and left-contort corolla aestivation.
Given the likely hybrid origin of this lineage and interme-
diate (chimeric) morphologies of species (see Tripp & al.,
2013b), it is difficult to place this lineage in either Acantheae or
Ruellieae and, as such, a new tribe is proposed here and de-
scribed formally below.
Barlerieae. –This lineage comprises 13 genera and ca.
500 species, with most of the species diversity occurring in two
widespread genera: the largely Paleotropical Barleria and the
Pantropical Lepidagathis. Confirmed and putative members
of Barlerieae share the synapomorphy of quincuncial corolla
aestivation (Scotland & Vollesen, 2000; McDade & al., 2008;
Darbyshire & al., 2019a) (Fig. 5B), but they are otherwise
morphologically diverse. For example, species may bear four
or five androecial units, comprising variously two stamens plus
two or three staminodes, or four stamens with or without one
staminode. When there are four stamens, they may all be bithe-
cous or may be configured with two bithecous + two monothe-
cous. With the exception of Barleria (Comito & al., in rev.),
genera of Barlerieae are among the least-studied lineages of
Acanthaceae from a molecular phylogenetic perspective, with
several having never been sequenced, and so the circumscription
of this tribe must be considered provisional (Darbyshire & al.,
2019a). Following further studies, it may be possible to recog-
nize subtribes, with morphological data suggesting at least three
taxa: (1) Barleria, with strongly zygomorphic calyces that are 4-
lobed due topartial or complete fusion of the two anterior lobes;
corollas that are variously arranged from subrotate to strongly
zygomorphic but always lacking a hooded upper lip; globose,
tricolporate, coarsely reticulate pollen; and an androecium usu-
ally of two fully developed bithecous stamens and either two
minute stamens that seem to function for self-pollination plus
one staminode, or three staminodes (Darbyshire & al., 2019a);
(2) Crabbea and allies, with ± actinomorphic, 5-lobed calyces;
weakly zygomorphic corollas without a hooded upper lip; glo-
bose to subprolate, tri- (or hexa-) porate, variously gemmate,
Fig. 5. Corolla aestivation types in Acanthaceae. Note that the “open”aestivation observed in some Acantheae is not illustrated here. A, Left-contort
(Avicennioideae in part, Thunbergioideae in part, Physacantheae, Whitfieldieae, Ruellieae); B, Quincuncial (Barlerieae); C, Ascending-cochlear
(Thunbergioideae in part, Acantheae, Andrographideae, Justicieae); D, Descending-cochlear (Nelsonioideae); E, Valvate (Avicennioideae in part);
F, Induplicate (Neuracantheae).
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verrucose, rugose to coarsely reticulate pollen; and an androe-
cium of four bithecous stamens (Thulin, 2007; Onjalalaina &
Darbyshire, 2016); and (3) Lepidagathis and allies, with often
zygomorphic, 5-lobed or sometimes 4-lobed calyces due to
partial fusion of the two anterior lobes; bilabiate corollas with
a hooded upper lip; prolate, tricolporate, finely reticulate pol-
len; and an androecium of four bithecous stamens or two
bithecous + two monothecous stamens or two bithecous sta-
mens plus two staminodes (Kameyama, 2008; Champluvier
& Darbyshire, 2012).
Andrographideae. –This lineage, comprising ca. eight
genera and ca. 130 species, is unusual in Acanthaceae in being
restricted to tropical Asia. These genera share the synapomor-
phy of “daubenpollen”, i.e., pollen with the apertural margins
and/or surfaces conspicuously thickened and intricately or-
namented with conical spines (Scotland & Vollesen, 2000;
McDade & al., 2008). Although apparently not closely related
(McDade & al., 2008), taxa of Andrographideae can other-
wise closely resemble members of Justicieae, with these two
tribes sharing ascending-cochlear aestivation (Fig. 5C), two
stamens with or without two additional staminodes, and zygo-
morphic, often bilabiate corollas. However, in addition to the
unique pollen type of Andrographideae, they are usually also
distinguished from Justicieae by ovule and seed number: An-
drographideae typically have more than four ovules per ovary
and the capsule is usually 6–20-seeded whereas Justicieae
have two or four ovules/seeds per capsule. However, 4-seeded
capsules are rarely recorded in Andrographideae, specifically
occurring in Andrographis (Indoneesiella)andinSphincta-
canthus; the latter genus is only tentatively placed in Androgra-
phideae here and with reference only to the type, S. griffithii
(T.Anderson) Benth. & Hook.f. (see Hansen, 1985b; McDade
& al., 2018; and footnote in the key, below). Molecular phylo-
genetic studies on Andrographideae have been very limited to
date (McDade & al., 2008; Arolla & al., 2015), and generic cir-
cumscription is still in a state of flux (Deng & al., 2020). For
example, the genus Haplanthus was recently reinstated as
distinct from Andrographis based on morphological evidence
(Gnanasekaran & al., 2016).
Whitfieldieae. –This small lineage of eight genera and
ca. 33 species is confined to tropical Africa and Madagascar
(Grall & Darbyshire, 2021). Manktelow & al. (2001) first rec-
ognized the tribe Whitfieldieae to accommodate Whitfieldia
together with two Afro-Malagasy genera, Chlamydacanthus
and Lankesteria. McDade & al. (2008) recognized a strongly
supported core Whitfieldieae clade and found Lankesteria to
be weakly supported as sister to it: these clades are here treated
as subtribes, Whitfieldiinae and Lankesteriinae. Manktelow
& al. (2001) proposed several synapomorphies for Whit-
fieldieae, most notably the presence of concentric rings of
ridges protruding from the testa of the seeds and pollen with
a densely granular circular area surrounding the pores. The
concentric ridges on the seeds are easily observed in Whitfiel-
diinae where the seeds lack trichomes, but they are hidden by
the presence of dense hygroscopic trichomes in Lankesterii-
nae. Most species for which pollen has been sampled have
lenticular, bipororate pollen grains with ectoapertures that
are usually very large and pseudocolpi absent, similar to (but
homoplasious with) the “gürtelpollen”of Isoglossinae, Justi-
cieae (Manktelow & al., 2001; McDade & al., 2008). Excep-
tions are Whitfieldia elongata, which has pantofororate pollen,
and Lankesteria, which has triporate pollen with a reticulate
exine (Manktelow & al., 2001). Members of Whitfieldieae also
combine left-contort aestivation (Fig. 5A) and four androecial
elements (usually four stamens in Whitfieldiinae, two stamens
+ two staminodes in Lankesteriinae), without any basal fusion
of filaments and lacking a f ilament curtain. Ruellieae also have
left-contort aestivation, but in that tribe, all but four of the ge-
nera have a well-developed filament curtain (see below). We
note that Manktelow & al. (2001) reported imbricate aestiva-
tion in Chlamydacanthus, but we have observed only contorted
buds in that genus.
Neuracantheae. –This tribe comprises the enigmatic
Paleotropical genus Neuracanthus Nees (32 spp.). McDade &
al. (2008) found Neuracanthus to be monophyletic with strong
support but were unable to place it with certainty within the
phylogeny of Acanthaceae. Instead, it was found to be weakly
supported as sister to a clade comprising (Barlerieae + An-
drographideae) + Whitfieldieae. The proposed morphological
synapomorphy for Neuracanthus, and hence for tribe Neura-
cantheae, is a bilabiate calyx with three posterior lobes and
two anterior lobes (i.e., in a 3 + 2 pattern) (McDade & al.,
2008). The arrangement of the corolla is also unique among
Acanthaceae: the two posterior lobes are largely fused to form
a lobe similar in size and shape to each of the three anterior
lobes, and these four broad, shallow lobes are arranged in
a ± equidistant manner such that the limb is funnel-shaped
and appears only weakly zygomorphic (Bidgood & Brummitt,
1998). Other features are shared with members of Barlerieae
and thus tentatively support a close relationship with that tribe.
For example, presence of hygroscopic trichomes on the seeds
and exstipitate, 2- or 4-seeded capsules. The androecium is
composed of four didynamous stamens, the anterior pair be-
ing bithecous and the posterior pair monothecous, an arrange-
mentalsofoundinsomespeciesofLepidagathis in Barlerieae
(Bidgood & Brummitt, 1998). However, the pollen of Neura-
canthus, which is tricolporate with a perforate tectum, does
not closely resemble pollen of any its putative relatives. The
corolla aestivation pattern of Neuracanthus is described as
induplicate by Balkwill & Welman (2000), in which the co-
rolla lobes are folded inwards at the margin and do not overlap
(Fig. 5F). This represents a unique aestivation pattern in
Acanthaceae. Attempts by the current authors to confirm this
from herbarium material have been inconclusive (I. Darbyshire
and T.F. Daniel, pers. obs.).
Ruellieae. –With 37 genera and ±1200 species, Ruel-
lieae are pantropical to temperate plants that vary tremendou-
sly in growth form, floral morphology, and ecology. Although
members of Ruellieae are primarily caulescent herbs (acaules-
cent in a few species) or shrubs, plants of Trichanthera and
Bravaisia are fully arborescent trees up to at least 9 m tall, ex-
tending to 20–25 m tall in Bravaisia integerrima (Spreng.)
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Standl., Trichanthera corymbosa Leonard, and Trichanthera
gigantea (Bonpl.) Nees (Daniel, 1998, 2015b). Among Acan-
thoideae, Ruellieae are second only to Justicieae in species
richness. Ruellieae are globally widespread, with the diverse
genera Ruellia and Strobilanthes dominating the Western and
Eastern Hemispheres, respectively, in taxonomic diversity.
Ruellieae have been the focus of detailed phylogenetic investi-
gation (Tripp & al., 2013a). Synapomorphies for the tribe in-
clude (1) presence of a filament curtain (evolutionarily lost in
some members), (2) left-contort corolla aestivation (Fig. 5A),
(3) presence of hygroscopic trichomes that cover seed surfaces
(these reduced to the seed margins in some genera and/or spe-
cies), and (4) bifid, filiform stigma lobes in which the dorsal
lobe is often partially or fully reduced. Within Acanthoideae,
only members of Whitfieldieae similarly have left-contort co-
rolla aestivation, but genera within that clade possess several
other features that separate them from Ruellieae (e.g., concen-
tric ridges on seed surfaces and capitate stigmas). Compared to
many other lineages of Acanthaceae, the number of seeds per
fruit is exceptionally diverse in Ruellieae, ranging from 2 to over
36 per capsule; seed number may vary markedly even within a
single genus (e.g., Ruellia). Most Ruellieae have flowers with
four stamens, but two stamens plus two staminodes are not un-
common. Ruellieae are most likely to be confused with Justi-
cieae, the sister lineage, with which they share pollen bearing
pseudocolpi in many taxa. There is no readily available macro-
morphological feature to differentiate the two tribes beyond
corolla aestivation: left-contort in Ruellieae and ascending-
cochlear in Justicieae. However, members of Justicieae more
commonly have 2 (vs. 4) stamens and lack a filament curtain
(but note that Asystasia and allies within Graptophyllinae have
four stamens, see below).
Justicieae. –With ca. 100 currently recognized genera
and at least 2000 species, Justicieae are the largest of the major
sublineages of Acanthaceae. The work of McDade & al. (2000b,
2021) supports the monophyly of Justicieae consisting of four
major clades: the Pseuderanthemum lineage, Isoglossinae, the
Tetramerium lineage, and the Justicioids, with Isoglossinae fur-
ther subdivided by McDade & al. (2021) into Isoglossinae s.str.
and the Ptyssiglottis lineage. The major clades of McDade & al.
(2000b, 2021) are here treated formally among five subtribes:
Graptophyllinae, Isoglossinae, Monotheciinae, Tetrameriinae,
and Justiciinae. Justicieae are marked by the presence of tricol-
porate, hexapseudocolpate pollen, a morphology not known in
other Acanthaceae. This pollen is known from all major lineages
of Justicieae, possibly excepting Isoglossinae (Kiel & al., 2006;
McDade & al., 2021), with subsequent evolutionary changes in
pollen morphology occurring in all subtribes (Kiel & al., 2017,
2018; McDade & al., 2021). Isoglossinae are marked by “gürtel-
pollen”, i.e., bipororate (more rarely tri- or tetrapororate), usually
lenticular pollen with a pronounced marginal girdle. Among
Justiciinae some species retain tricolporate hexapseudocolpate
pollen but in many other species, particularly NW Justiciinae,
exine ornamentation and aperture number depart considerably.
In contrast to Ruellieae, species of which have a wide range in
seed number, members of Justicieae typically have two to four
seeds per capsule. Justicieae are also notable for their androecial
diversity, with staminal elements ranging from two to four, to-
gether with additional innovations (see below). Plants of Grapto-
phyllinae have four staminal elements, either as four stamens or
as two stamens + two staminodes. In contrast, all other Justicieae
have just two stamens and no staminodes, with the exception of
Chalarothyrsus (Tetrameriinae), which has four stamens. Spe-
cies of Justiciinae have corollas with a rugula (i.e., a medial fur-
row in the internal surface of the dorsal corolla lip and tube in
which the style lies during anthesis). The rugula is lost secon-
darily in some genera including Dicliptera and Hypoestes. Addi-
tionally, taxa of Justiciinae often have “anther complexity”in
which the thecae are not parallel, not evenly inserted on the fila-
ment (i.e., the pair are offset from one another), and/or are basally
awned or spurred (Kiel & al., 2017, 2018). Unevenly inserted
and/or oblique thecae are also frequent in Isoglossinae but there
the thecae are not awned or spurred (Darbyshire, 2009; Darby-
shire & al., 2011; McDade & al., 2021). Unevenly inserted and
oblique thecae are uncommon elsewhere in Justicieae, although
awned or otherwise appendaged thecae are widespread in Grap-
tophyllinae and occasional in Monotheciinae (Darbyshire & al.,
2019c; McDade & al., 2021). There are, at present, no known
morphological synapomorphies for Tetrameriinae or Monothe-
ciinae (McDade & al., 2018, 2021).
Generic delimitation within Acanthaceae. —Histori-
cally, generic delimitation has been a challenge owing to com-
plex patterns of morphological variation exacerbated by scant
collections and a paucity of systematists and taxonomists work-
ing in such a diverse family. More recently, these challenges
have been compoundedby a paucity of recentlycollected mate-
rial for molecular phylogenetic study. Although resolving the
entirety of outstanding issues concerning relationships within
and among genera is beyond the scope of the present work,
we take the opportunity to remark on some of our most persis-
tent challenges in the footnotes to the keys, below. Genera of
Acanthaceae have traditionally been delimited based on mor-
phological traits, with important characters including calyx
and corolla morphology, number and characteristics of the an-
droecial units, variation in pollen type, number of ovules/seeds,
and capsule morphology. Although many of these traits are
phylogenetically informative, reliance on variation in floral mor-
phology to delimit genera has, in some cases, yielded unsatis-
factory generic delimitation owing to rampant homoplasy (e.g.,
Daniel & al., 2008; Tripp & Manos, 2008; Côrtes & al., 2015).
This also applies to numerous instances of segregate genera now
known to be nested within a larger genus (e.g., Ruellia,Tripp,
2007). Recent molecular studies, involving denser sampling
than previously achieved, have revealed the magnitude of the
problem in some parts of the family. In Tetrameriinae, McDade
& al. (2018) refer to a “clade complex”, analogous to a species
complex but in this case of clades that are very distinctive with
regard to molecular data but show no notable macromorphologi-
cal differences based on current evidence. In Justiciinae, Kiel &
al. (2017, 2018) proposed several options for radical changes to
generic circumscription in view of the gross non-monophyly of
Justici a, with subsequent studies inclining towards a narrower
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circumscription of genera (Darbyshire & al., 2019c, 2020, in
press).
Elsewhere in the family, genera within some clades such
as Barlerieae (Onjalalaina & Darbyshire, 2016), Whitfieldieae
(Grall & Darbyshire, 2021), Isoglossinae (Kiel & al., 2006;
McDade & al., 2021), and Graptophyllinae (McDade & al.,
2021) remain poorly delimited morphologically. Excessive
segregation of genera is sometimes linked to geography and
to taxonomists who have focused on those regions. This is
most notable in Madagascar, where many of the endemic ge-
nera, as currently delimited, are not well differentiated from
continental African genera (Onjalalaina & Darbyshire, 2016).
Indeed, detailed molecular studies in Ruellieae showed that all
three genera of Ruellieae that were previously considered to
be endemic to Madagascar were nested within African or pan-
tropical genera (Tripp & al., 2013a). Other genera have long
been in flux. For example, the extensive variation in pollen
morphology among species of Strobilanthes led Bremekamp
(1944) to subdivide this lineage into some 54 genera; most of
these names have subsequently been synonymized back into
Strobilanthes (e.g., Wood & Scotland, 2009; Hu & al., 2011;
Tripp & al., 2013a; Wood, 2014).
In sum, the most pressing challenge now facing those
studying Acanthaceae is to provide a robust generic framework
for the family. In the current work, we place all accepted (and
disputed) genera within a revised classification of the family.
Although this represents our best prediction of relatedness based
on available evidence, we emphasize that several issues persist
and some aspects of the classification presented below will be
further revised following inclusion of as yet unsampled genera
in ongoing and future phylogenetic studies and analyses.
■TAXONOMIC TREATMENT OF
ACANTHACEAE
The revised classification of Acanthaceae is organized
by subfamily followed by tribe, subtribe, then genus. Sub-
families, tribes, and subtribes are organized phylogenetically.
Genera are organized alphabetically (see Appendix 2 for a
proposed linear phylogenetic sequence for the genera). Fol-
lowing taxon names, a “ch”denotes changes since, and devi-
ations from, Scotland & Vollesen (2000), including additional
genera. We do not mark lineages that have changed rank (e.g.,
Barleriinae to Barlerieae) or that have been subdivided (e.g.,
the subtribes of Justicieae and Ruellieae) since Scotland &
Vollesen (2000). A “mol”denotes that the taxon has been inclu-
ded in a published phylogenetic study based on molecular se-
quence data. A “prov”indicates that the classification should be
considered provisional.
Following each genus is a geographical code to represent
our best understanding of approximate native distributions of
genera, as follows: AA (Southeast Asia, Australasia, Oceania,
and greater Pacific), AF (continental sub-Saharan Africa and
associated islands but excluding Madagascar and the Mascar-
enes), AR (Arabian Peninsula including Socotra, through Iran),
EU (Europe, Mediterranean region, Middle East), IC (India and
Pakistan through China and Japan), MA (Madagascar and the
Mascarenes), NW (New World), PAN (representation in both
the OW and the NW). Instances where there is uncertainty sur-
rounding native status of taxa in a given region, for example,
whether Nelsonia is or is not native to the NW, we default to
the former. Dichotomous keys are organized by taxonomy as
well as by geography. For purposes of the geographical keys to
genera, several regions were combined. We present a total of
three keys: (1) AA + IC, (2) AF + AR + EU + MA, and (3) NW.
I. The classification
ACANTHACEAE Juss.
NELSONIOIDEAE Pfeiff. (6 genera)
Anisosepalum E.Hossain (AF); mol
Aymoreana Braz, T.F.Daniel & Kiel (NW); ch, mol
Elytraria Michx. (PAN); mol
Nelsonia R.Br. (PAN); mol
Saintpauliopsis Staner (AF, MA); mol
Staurogyne Wall. (PAN); mol
AVICENNIOIDEAE Miers (1 genus)
Avicennia L. (PAN); ch, mol
THUNBERGIOIDEAE T.Anderson
Mendoncieae Meisn. (2 genera)
Anomacanthus R.D.Good (AF)
Mendoncia Vell. ex Vand. (AF, MA, NW); mol
Thunbergieae Dumort. (3 genera)
Meyenia Nees (IC)
Pseudocalyx Radlk. (AF, MA); mol
Thunbergia Retz. (AA, AF, IC, MA); mol
ACANTHOIDEAE Eaton
Acantheae Dumort.
Acanthinae Nees (8 genera)
Acanthopsis Harv. (AF); mol
Acanthus L. (AA, AF, AR, EU, IC); mol
Blepharis Juss. (AA, AF, IC); mol
Crossandra Salisb. (AF, AR, IC, MA); mol
Crossandrella C.B.Clarke (AF); mol
Cynarospermum Vollesen (IC); mol
Sclerochiton Harv. (AF); mol
Streptosiphon Mildbr. (AF); mol
Aphelandrinae Bremek. (7 genera)
Aphelandra R.Br. (NW); mol
Cyphacanthus Leonard (NW)
Holographis Nees (NW); mol
Neriacanthus Benth. (NW); mol
Salpixantha Hook. (NW); mol
Stenandriopsis S.Moore (AF, MA); ch, mol
Stenandrium Nees (NW); mol
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Physacantheae E.Tripp & I.Darbysh., tr. nov. (1 genus)
Physacanthus Benth. (AF); ch, mol
Neuracantheae Reveal (1 genus)
Neuracanthus Nees (AA, AF, IC, MA); ch, mol
Barlerieae Nees (13 genera)
Barleria L. (PAN); mol
Barleriola Oerst. (NW)
Borneacanthus Bremek. (AA)
Boutonia DC. (MA)
Chroesthes Benoist (AA, IC)
Crabbea Harv. (AF); mol
Hulemacanthus S.Moore (AA)
Lasiocladus Bojer ex Nees (MA); ch, mol
Lepidagathis Willd. (PAN); mol
Pericalypta Benoist (MA); ch
Podorungia Baill. (MA); ch
Pseudodicliptera Benoist (MA); ch, mol
Schaueriopsis Champl. & I.Darbysh. (AF); ch, mol
Andrographideae Endl. (8 genera)
Andrographis Wall. ex Nees (AA, IC); mol
Diotacanthus Benth. (IC)
Graphandra J.B.Imlay (AA)
Gymnostachyum Nees (AA, IC); mol
Haplanthodes Kuntze (IC)
Haplanthus Nees (AA, IC); ch
Phlogacanthus Nees (AA, IC); mol
Sphinctacanthus Benth. (IC); ch, prov
Whitfieldieae Bremek. ex Reveal
Lankesteriinae I.Darbysh. & E.Tripp, subtr. nov.
(1 genus)
Lankesteria Lindl. (AF, MA); ch, mol
Whitfieldiinae I.Darbysh. & E.Tripp, subtr. nov.
(7 genera)
Camarotea Scott Elliot (MA); ch, mol
Chlamydacanthus Lindau (AF, MA); ch, mol
Forcipella Baill. (MA); ch, mol
Leandriella Benoist (MA); ch, mol
Vindasia Benoist (MA); ch
Whitfieldia Hook. (AF); ch, mol
Zygoruellia Baill. (MA); ch, mol
Ruellieae Dumort.
Erantheminae Nees (5 genera)
Brunoniella Bremek. (AA); mol
Eranthemum L. (AA, IC); mol
Kosmosiphon Lindau (AF); mol
Leptosiphonium F.Muell. (AA); mol
Pararuellia Bremek. & Nann.-Bremek. (AA, IC); mol
Dinteracanthinae E.Tripp & I.Darbysh. (1 genus)
Dinteracanthus Schinz (AF); ch, mol
Ruelliinae Nees (5 genera)
Acanthopale C.B.Clarke (AA, MA); mol
Calacanthus T.Anders. ex Benth. (IC); mol
Dischistocalyx T.Anderson ex Benth. (AF); mol
Ruellia L. (PAN); mol
Satanocrater Schweinf. (AF); mol
Trichantherinae Benth. & Hook.f. (6 genera)
Bravaisia DC. (NW); mol
Louteridium S.Watson (NW); mol
Sanchezia Ruiz & Pav. (NW); mol
Suessenguthia Merxm. (NW); mol
Trichanthera Kunth (NW); mol
Trichosanchezia Mildbr. (NW); mol
Strobilanthinae T.Anderson (1 genus)
Strobilanthes Blume (AA, IC); mol
Hygrophilinae Nees (2 genera)
Brillantaisia P.Beauv. (AF, MA); mol
Hygrophila R.Br. (PAN); mol
Petalidiinae Benth. & Hook.f. (6 genera)
Duosperma Dayton (AF); mol
Dyschoriste Nees (PAN); mol
Echinacanthus Nees (IC, AA); mol
Petalidium Nees (AF, IC); mol
Ruelliopsis C.B.Clarke (AF); mol
Strobilanthopsis S.Moore (AF); mol
Mcdadeinae E.Tripp & I.Darbysh. (1 genus)
Mcdadea E.Tripp & I.Darbysh. (AF); ch, mol
Phaulopsidinae E.Tripp & I.Darbysh. (1 genus)
Phaulopsis Willd. (PAN); mol
Mimulopsidinae E.Tripp (4 genera)
Eremomastax Lindau (AF); mol
Heteradelphia Lindau (AF); mol
Mellera S.Moore (AF); mol
Mimulopsis Schweinf. (AF, MA); mol
Ruellieae incertae sedis (3 genera)
Diceratotheca J.R.I.Wood & Scotland (AA); ch
Stenothyrsus C.B.Clarke (AA)
Xylacanthus Aver. & K.S.Nguyen (AA); ch
Justicieae Dumort.
Graptophyllinae T.Anderson (27 genera)
Afrofittonia Lindau (AF); mol
Asystasia Blume (AA, AF, AR, IC, MA); mol
Ballochia Balf.f. (AR); mol
Chamaeranthemum Nees (NW); mol
Chileranthemum Oerst. (NW); mol
Codonacanthus Nees (IC); mol
Cosmianthemum Bremek. (AA, IC); mol
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Filetia Miq. (?AF, AA); mol
Glossochilus Nees (AF); mol
Graptophyllum Nees (AA, AF); mol
Herpetacanthus Nees (NW); mol
Isotheca Turrill (NW)
Linariantha B.L.Burtt & R.M.Sm. (AA)
Mackaya Harv. (AF, IC); mol
Odontonema Nees (NW); mol
Oplonia Raf. (MA, NW); mol
Phialacanthus Benth. (AA, IC)
Pranceacanthus Wassh. (NW); mol
Pseuderanthemum Radlk. (PAN); mol
Psilanthele Lindau (NW); mol
Pulchranthus V.M.Baum, Reveal & Nowicke (NW); mol
Ruspolia Lindau (AF, MA); mol
Ruttya Harv. (AF, AR, MA); mol
Sapphoa Urb. (NW)
Spathacanthus Baill. (NW); mol
Thysanostigma J.B.Imlay (AA)
Wuacanthus Y.F.Deng, N.H.Xia & H.Peng (IC); ch, mol
Monotheciinae Lindau (8 genera)
Ambongia Benoist (MA); prov
Calycacanthus K.Schum. (AA); mol
Champluviera I.Darbysh., T.F.Daniel & Kiel (AF); ch, mol
Cyclacanthus S.Moore (AA); prov
Jadunia Lindau (AA); mol
Marcania J.B.Imlay (AA); mol
Monothecium Hochst. (AF, IC); mol
Ptyssiglottis T.Anderson (AA, IC); mol
Isoglossinae Lindau (7 genera)
Brachystephanus Nees (AF, MA); mol
Celerina Benoist (MA)
Isoglossa Oerst. (AA, AF, AR, IC, MA); mol
Melittacanthus S.Moore (MA); mol
Sebastiano-Schaueria Nees (NW); mol
Stenostephanus Nees (NW); mol
Sphacanthus Benoist (MA); ch, mol
Tetrameriinae T.F.Daniel, Kiel & McDade, subtr. nov.
(27 genera)
Ancistranthus Lindau (NW); mol
Angkalanthus Balf.f. (AR); mol
Anisacanthus Nees (NW); mol
Aphanosperma T.F.Daniel (NW); mol
Carlowrightia A.Gray (NW); mol
Cephalophis Vollesen (AF); ch, prov
Chalarothyrsus Lindau (NW); mol
Chlamydocardia Lindau (AF); mol
Chorisochora Vollesen (AF, AR); mol
Clinacanthus Nees (AA, IC); mol
Ecbolium Kurz (AF, AR, IC, MA); mol
Fittonia Coem. (NW); mol
Gypsacanthus E.J.Lott, V.Jaram. & Rzed. (NW); mol
Henrya Benth. (NW); mol
Hoverdenia Nees (NW); mol
Kudoacanthus Hosok. (IC); ch, mol
Leptostachya Nees (AA, IC); ch, prov
Megalochlamys Lindau (AF, AR); mol
Mexacanthus T.F.Daniel (NW); mol
Mirandea Rzed. (NW); mol
Pachystachys Nees (NW); mol
Populina Baill. (MA); mol
Schaueria Nees (NW); mol
Tetramerium Nees (NW); mol
Thyrsacanthus Moric. (NW); ch, mol
Trichaulax Vollesen (AF); mol
Yeatesia Small (NW); mol
Justiciinae Nees (23 genera)
Anisostachya Nees (AF, MA); ch, mol
Anisotes Nees (AF, AR, MA); mol
Ascotheca Heine (AF); mol
Cephalacanthus Lindau (NW); mol
Clistax Mart. (NW); mol
Dasytropis Urb. (NW); prov
Dichazothece Lindau (NW); prov
Dicladanthera F.Muell. (AA); prov
Dicliptera Juss. (PAN); mol
Harpochilus Nees (NW); mol
Hypoestes Sol. ex R.Br. (AA, AF, AR, IC, MA); mol
Justicia L. (PAN); mol
Kenyacanthus I.Darbysh. & Kiel (AF); ch, mol
Megaskepasma Lindau (NW); mol
Meiosperma Raf. (AF, IC); ch, mol
Metarungia Baden (AF); mol
Pogonospermum Hochst. (AF); ch, mol
Poikilacanthus Lindau (NW); mol
Rhinacanthus Nees (AA, AF, AR, IC, MA); mol
Rungia Nees (AA, AF, AR, IC, MA); mol
Trichocalyx Balf.f. (AR); mol
Vavara Benoist (MA); ch
Xerothamnella C.T.White (AA); mol
Justicieae incertae sedis (5 genera)
Dolichostachys Benoist (MA); ch
Ichthyostoma Hedrén & Vollesen (AF); mol
Samuelssonia Urb. & Ekman (NW)
Streblacanthus Kuntze (NW); mol
Tessmanniacanthus Mildbr. (NW)
ACANTHACEAE incertae sedis (1 genus)
Ritonia Benoist (MA); ch
Excluded names. —Gymnophragma Lindau was validly
published with two syntypes (both collected by C. Leder-
mann, Papua New Guinea) described in the protologue. How-
ever, neither appear to be extant, and there is apparently no
additional extant material representing this genus. Based on
the protologue it is furthermore unclear as to what taxon this
name likely applies. We thus here exclude the name.
Version of Record 17
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Idiacanthus Leonard was not validly published but rather ap-
plied only to herbarium material (McDade & al., 2008). It is likely
that this name refers to Stenostephanus (McDade & al., 2008).
Schwabea Endl. was previously treated as congeneric with
Monechma Hochst. but the description in the protologue does
not fit with the latter “genus”(now segregated into Meiosperma
and Pogonospermum), most notably in the androecium of four
stamens. The genus was described from cultivated plants
grown from an unnumbered collection made by T. Kotschy
in “Nubia”, and no extant original material has been traced.
Sericospora Nees was based on a single species, S. crinita
Nees, which belongs within Justicieae, but the type material at
GZU is a mixed collection with one of the shoots being non-
Acanthaceae. It is possible that the capsule and seeds in the
packet do not pertain to the shoot of Acanthaceae. The plant
may belong within Justicia but this requires confirmation.
Strobilacanthus Griseb. probably refers to cultivated Cros-
sandra (McDade & al., 2005).
II & III. Dichotomous keys
Here, we present a series of keys (12 in total) for identifi-
cation of Acanthaceae. Keys to subfamilies, tribes, and genera
(Part II) are followed by geographical keys to genera (Part III).
Specifically, Part II (9 keys) consists of: Key to the subfamilies
of Acanthaceae, Key to the tribes of Acanthoideae,Key to the ge-
nera of Nelsonioideae, Key to the genera of Thunbergioideae,
Key to the genera of Acantheae, Key to the genera of Barleri-
eae, Key to the genera of Andrographideae, Key to the genera
of Whitfieldieae, and Key to the genera of Ruellieae. Part III
(3 keys) consists of: Key to genera in Africa, Madagascar,
the Mediterranean region, and the Arabian Peninsula; Key to
genera in Asia and Australasia (excluding the Arabian Peninsula
and Mediterranean region); and Key to genera in the Americas.
InPartII,theonlymajorlineageforwhichwehavenotyetpro-
duced a worldwide key to the genera is Justicieae, which re-
mains taxonomically problematic. Genera of Justicieae are,
however, included within the geographical keys in Part III.
This effort represents the first such attempt since Lindau
(1895) to introduce globally useful keys but has not been with-
out challenges. These challenges arise because there remains
much work to be done to adequately resolve generic circum-
scription in several lineages of the family, with many future
generic changes likely. We have tried, where possible, to ad-
dress most of the known exceptions to typical morphological
features of a genus either through use of endnotes (numbers in
square brackets) or, in some cases, through separation of a parti-
cular taxon or group of taxa elsewhere in the key.
At the generic rank, several morphological characters,
such as the number of stamens, the presence or absence of sta-
minodes, the number, arrangement and ornamentation of an-
ther thecae, the number of ovules and seeds, and the arran-
gement of the calyx and corolla, are both taxonomically infor-
mative and easily observable. As such, these characters are
broadly employed in the dichotomous keys below, even when
exceptions require that genera be keyed more than once. This
helps to avoid the use of less readily observable characters.
However, in some instances, we have needed to resort to using
more technical characters (e.g., corolla aestivation, pollen mor-
phology) where such features are of primary importance in
taxon delimitation. Future attempts to delimit taxa may avoid
the use of such subtle features through development of multi-
access keys to the genera.
The following set of keys emphasizes taxa native to res-
pective geographical regions. Thus, species that have been intro-
duced to a given region but are not native there are generally not
included in the key to that region. Geographical ranges are in-
cluded in the keys in Parts II and III where they are useful in
the separation of morphologically similar genera or where taxa
have a notably restricted distribution; in Part III, if specific ge-
ography is not listed, it can be taken that the genus is wide-
spread in that geographical region.
For the 12 keys presented below, we define the following
terms:
(1) Types of corolla aestivation,ortheorientationof
petals to one another during the mature bud stage: refer to Fig. 5
for a schematic of all types used in keys.
(2) A filament curtain is a physical partition within the
corolla formed by elaboration of the synstapetal zone to form
flanges of tissue that partition the corolla obliquely into two
compartments and enclose a nectar chamber behind this phys-
ical partition.
(3) A rugula is a groove formed by elaborations of the in-
ner surface of the corolla, often derived from veins along the
dorsal side of the corolla to form a channel that generally re-
tains the style within the tube and oftentimes upper lip. This
structure is sometimes referred to as a “stylar furrow”.
(4) Fracturing placentae refer to fruits in which the pla-
centae and retinacula fracture away from the capsule walls
during fruit dehiscence. This is sometimes referred to as “elas-
tic dehiscence”in other works. In some cases, the lateral walls
of the capsule (which can be modified and thinned) also rup-
ture as the placentae fracture.
(5) Cystoliths are mineralized structures of unknown
substance in Acanthaceae (putatively calcium oxalate) that are
visible generally as hyaline or white streaks or dots on dried
herbarium material on the upper and/or lower leaf surfaces,
and sometimes on other vegetative surfaces (e.g., commonly on
stems). These structures characterize Acanthoideae except for
members of Acantheae and Physacantheae.
(6) Nototribic flowers have stamens positioned near or
appressed to the upper lip of the corolla and anthers dehisc-
ing toward the lower lip; this is the most typical condition in
Acanthaceae. Sternotribic flowers have stamens positioned
near or appressed to the lower lip of corolla and anthers dehisc-
ing toward the upper lip. Pleurotribic flowers have stamens
positioned between the two lips of the corolla and anthers de-
hiscing toward the center of the floral axis and each other.
(7) Zygomorphic corollas are those with an overall single
plane of symmetry (i.e., bilaterally symmetric). Bilabiate co-
rollas are zygomorphic but with two distinct lips, i.e., an upper
and a lower lip.
18 Version of Record
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(8) Hygroscopic trichomes are typical of seed surfaces
on many genera of Acanthaceae; such trichomes become in-
flated and elongated when moistened and many are addition-
ally mucilaginous when inflated.
II. Keys to the subfamilies, tribes, and genera
of Acanthaceae
Key to the subfamilies of Acanthaceae
1 Fruit a capsule with seeds held on hooked retinacula (retinacula
malformed or not discernible in Aphanosperma and Chalarothyr-
sus and seeds permanently retained in capsule valves); cystoliths
present or if absent then anthers monothecous ....... Acanthoideae
1 Fruit a capsule or a drupe; if a capsule, then without hooked reti-
nacula; cystoliths absent; anthers bithecous ................................ 2
2 Mangrove trees or shrubs with pneumatophores; fruit a leathery
1-seeded capsule ................................................... Avicennioideae
2 Herbs, shrubs or lianas, not mangrove trees or shrubs, pneumatophores
absent; fruit a capsule with 2 or more seeds, or a 1–2-seeded drupe ... 3
3 Herbs or shrubs, not twining; paired bracteoles present or absent
but never large and conspicuous; flowers usually alternate or spi-
rally arranged in few- to many-flowered inflorescences; calyx
deeply 4- or 5-lobed;fruit a many-seeded (usually >10 seeds)capsule
..................................................................................... Nelsonioideae
3 Climbing herbs or lianas, less frequently free-standing shrubs or
perennial herbs; flowers subtended by conspicuous clasping or
partially connate (at anthesis) paired bracteoles; flowers solitary
or in fascicles or racemes of mostly opposite flowers, neverspirally
arranged; calyx a subentire or undulate rim or with irregular teeth,
or shallowly 5-lobed; fruit either a 1–2-seeded drupe or a 2–4-
seeded woody capsule....................................... Thunbergioideae
Key to the tribes of Acanthoideae
1 Cystoliths absent; stamens 4, monothecous................................. 2
1 Cystoliths present; stamens 2 or 4, if 4 then at least 2 of these
bithecous...................................................................................... 3
2 Calyx long-tubular, cylindrical to inflated; pollen colporate; capsule
with more than 4 seeds; corolla aestivation left-contort.....................
...............................................................................Physacantheae [1]
2 Calyx not as above; pollen colpate; capsule with up to 4 seeds; co-
rolla aestivation ascending-cochlear ............................ Acantheae
3 Calyx strongly bilabiate, with a 2-lobed or -toothed anterior lip and
a 3-lobed or -toothed posterior lip; androecium usually of 2 bithe-
cous stamens and 2 monothecous stamens (rarely 4 bithecous sta-
mens); corolla with a funnel-shaped limb comprising equal anterior
and lateral lobes and partially (or almost completely) fused dorsal
pair of lobes, not strongly bilabiate........................Neuracantheae
3 Above combination of characters lacking;if androecium of 2 bithe-
cous stamens and 2 monothecous stamens then corolla strongly
bilabiate ......................................................................................... 4
4 Corolla with left-contort aestivation in bud ................................. 5
4 Corolla with either quincuncial or ascending-cochlear aestivation
in bud ........................................................................................... 6
5 Corolla tube with a f ilament curtain present (in all but 4 genera);
seeds with trichomes either covering entire surfaces or along rim,
often hygroscopic, seed surface without concentric ridges............
........................................................................................Ruellieae
5 Corolla tube lacking a filament curtain; seeds sculptured with con-
centric ridges at least towards the rim, lacking trichomes, or if hy-
groscopic trichomes covering the seed surface (Lankesteria only)
then with the unique combination of: corolla salverform with a
long narrowly cylindrical tube and a spreading 5-lobed limb, some-
times with the sinus between the anterior pair of lobes broader than
the other sinuses ........................................................Whitfieldieae
6 Corolla with quincuncial aestivation.............................Barlerieae
6 Corolla with ascending-cochlear aestivation................................ 7
7 Capsule 6–20-seeded or rarely 4-seeded; pollen with apertural
margin or surface conspicuously thickened and often intricately or-
namented with conical spines, pseudocolpi absent........................
......................................................................... Andrographideae
7 Capsule 2- or 4-seeded; pollen variable but without conspicuously
thickened and ornamented apertural margins or surfaces, pseudo-
colpi often present .........................................................Justicieae
Key to the genera of Nelsonioideae [2]
1 Peduncles (if present) bearing alternate to spirally arranged, clasp-
ing scale-like sterile bracts; bracts sclerophyllous to coriaceous;
leaves alternate and diffuse along stems or in rosettes or whorls
either basally or terminating branches; stigma scarcely divided,
touch-sensitive, folded over and enclosing anthers in undisturbed
flowers, becoming erect when touched............................Elytraria
1 Peduncles (if present) without clasping scale-like bracts; bracts
membranous or foliaceous; leaves opposite (sometimes suboppo-
site or alternate in Nelsonia and Staurogyne), at least some pairs dis-
persed along the stems; stigma usually conspicuously lobed, neither
folded over nor enclosing anthers, no t t ouch-sensitive......... ........... 2
2 Bracteoles absent; inflorescence of dense ± cylindrical spikes with
imbricate bracts; calyx 4-lobed, the anterior lobe with bif id apex
(rarely more deeply divided into 5 lobes); stamens 2, staminodes
absent............................................................................... Nelsonia
2 Bracteoles present; inflorescence variable but if spikes cylindrical
then not so dense (except in Anisosepalum); calyx 5-lobed; sta-
mens 4, adaxial staminode often also present (rarely reduced to 2
stamens + 2–3 staminodes) .......................................................... 3
3 Pairs of bracteoles inserted below receptacle, not adnate to it or to
base of calyx tube (leaves not ternate and corollas usually less than
3 cm long)....................................................................Staurogyne
3 Pairs of bracteoles partially adnate to receptacle and sometimes also
to base of calyx tube (or if bracteoles sometimes free in Anisosepalum
lewallei, then leaves mostly ternate and corollas 3–4 cm long) ....... 4
4 Calyx lobes subequal but similar to one another and not hidden by
bracteoles; ovary asymmetric with style arising on one side, stigma
1-lobed, lobe apically subcapitate; Brazil ................... Aymoreana
4 Lateral 2 calyx lobes markedly shorter than other lobes and often
hidden by the bracteoles; gynoecium not with the above combina-
tion of characters; Africa, Madagascar ........................................ 5
5 Plants delicate trailing herbs; petiole usually longer than leaf blade;
anther thecae with a basal appendage, this often forked; corolla wid-
ened almost to the base into a campanulate throat, palate of lower lip
not bullate, i.e., without raised bosses ...................... Saintpauliopsis
5 Plants erect or procumbent herbs or subshrubs; petiole usually
shorter than leaf blade; anther thecae with basal appendages absent
or short, apiculate, not forked; corolla with a cylindrical basal tube,
and ± gradually widened throat, not appearing campanulate, palate
of lower lip bullate, i.e., with raised bosses................ Anisosepalum
Key to the genera of Thunbergioideae
1 Fruit a fleshy drupe with 1 or 2 seeds.......................................... 2
1 Fruit a woody capsule with 2 or 4 seeds ...................................... 3
2 Drupe 2-seeded, large (3–10 cm in diam.) ........... Anomacanthus
2 Drupe 1-seeded, not so large .......................................Mendoncia
3 Stigma ± equally 2-lobed, each lobe subdivided into 2 unequal
lobes; pollen 7–9-lobate and -colpate .............................. Meyenia
3 Stigma funnel-shaped, capitate, unequally 2-lobed or if equally
lobed then not subdivided; pollen spiraperturate and unlobed ....4
4 Anthers opening by apical pores; seed with a scar on the proximal
face; indumentum stellate, bracteoles with a dense orange, red or
mustard-yellow stellate indumentum covering the external surface
...................................................................................Pseudocalyx
Version of Record 19
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4 Anthers opening by longitudinal slits; seed hollow on the proximal
face; indumentum rarely stellate, bracteoles without a very dense or-
ange, red or mustard-yellow indumentum externally....Thunbergia
Key to the genera of Acantheae
1 Corolla regularly 5-lobed or bilabiate, not comprising a single lip.... 2
1 Corolla lobes comprising a single lip, entire or 3- or 5-lobed, held
either ventrally or dorsally, or if (rarely) not markedly 1-lipped [3]
then at least with the sinus between the 2 uppermost (outermost)
lobes clearly at a wider angle than that of the other sinuses ........ 8
2 Plants of tropical Africa and Madagascar ........ Stenandriopsis [4]
2 Plants of the Americas ................................................................. 3
3 Corolla zygomorphic, the lobes dissimilar in form ..................... 4
3 Corolla usually subactinomorphic, the lobes more or less similar in
form (or nearly zygomorphic with lobes of upper lip dissimilar
from those of lower lip in some Stenandrium) ............................ 6
4 Calyx deeply 3-partite.............................................Cyphacanthus
4 Calyx 5-par tite ............................................................................. 5
5 Leaves opposite (rarely subopposite), not quaternate; bracts entire or
dentate, green or often brightly colored; corollas rarely with linear
nectar guides, mostly 25–85 mm long; at least distal portion of fila-
ments of stamens usually exserted from corolla tube; pollen with
colpi not expanded or bifurcating (usually narrowed) toward poles,
interapertural exine usually heterogeneously sculptured; plants typi-
cally of wet habitats; widespread in NW..................Aphelandra [5]
5 Leaves opposite (rarely subopposite) or quaternate; bracts entire
and usually green; corolla often with colored linear nectar guides,
6.5–24 mm long (or if longer [to 40 mm], then plants with quater-
nate leaves); filaments of stamens often entirely included in corolla
tube; pollen with colpi sometimes expanded or bifurcating toward
poles, interapertural exine homogeneously sculptured; plants of
dry habitats; Mexico .................................................. Holographis
6 Pollen 3-colpate with each colpus longitudinally bisected by an
operculum (elongate band of exine), opercula either isolated within
the colpi (operculate) or connected at each end to the interapertural
exine (pontoperculate); Jamaica................................ Salpixantha [6]
6 Pollen 3-colpate with colpi not bisected by elongate bands of exine
or pollen pantoforate (i.e., sometimes in Stenandrium dulce)or
pollen pantoaperturate (rugate) with rugae arranged ± tangentially
or irregularly over surface or pollen 3-colpate and with prominent
margines and mesocolpial ridges (appearing 9-colpate); wide-
spread, but not in Jamaica............................................................ 7
7 Plants usually small, up to 25(–70) cm; leaves often borne at or
near ground level (plants acaulescent to subcaulescent); bracts usu-
ally green; widespread .............................................. Stenandrium
7 Plants usually shrubby, up to 1.5 m tall; leaves disposed along con-
spicuous stems; bracts whitish, pinkish, or reddish-brown; Central
America and South America...............................Neriacanthus [6]
8 Corolla tube twisted through 180°, the single corolla lip held dor-
sally, entire or 3-lobed; Tanzania.............................Streptosiphon
8 Corolla tube not twisted, corolla lip held ventrally, 3- or 5-lobed or
sometimes only undulate ............................................................. 9
9 Stamens included in corolla tube, anthers subsessile, not inserted
on a thickened flange ................................................................. 10
9 Stamens exserted from corolla tube, with flattened bone-like fila-
ments, inserted on a thickened flange ........................................ 11
10 Calyx 4-lobed, anterior lobe bifid; bracts not imbricate, smaller than
bracteoles; bracteoles conspicuous, elliptic or obovate, diverging
widely from inflorescence axis; corolla tube not narrowly cylindri-
cal, limb obscurely 5-lobed or erose ..........................Crossandrella
10 Calyx 5-lobed; bracts usually imbricate, larger than and enclosing
bracteoles; bracteoles linear to lanceolate, not diverging widely
from inflorescence axis; corolla tube narrowly cylindrical, limb
5-lobed........................................................................ Crossandra
11 Calyx 5-lobed; seeds sculpted with pectinate scales or concentric
rings; bracts, bracteoles and calyx lobes glumaceous ... Sclerochiton
11 Calyx 4-lobed; seeds either covered in hygroscopic trichomes,
puberulous or glabrous, or seeds tuberculate, without scales
or concentric rings; bracts, bracteoles and calyces only rarely
glumaceous ..................................... .................................... 12
12 Anterior pair of staminal filaments flattened and either with an ob-
tuse or acute tooth-like appendage or truncate to rounded towards
apex ventrally ............................................................................ 13
12 Anterior staminal filaments lacking appendages, if flattened then
gradually nar rowed towards apex .............................................. 14
13 Leaves opposite; flowers solitary or paired in leaf axils, each sub-
tended by 2 pairs of bracteoles, outer pair entire, inner pair trif id;
ovary without apical tufts of glandular trichomes; seeds tubercu-
late; India ............................................................ Cynarospermum
13 Leaves in pseudowhorls of (3) 4; inflorescences variable but not
with single or paired flowers in leaf axils; bracteoles entire or
toothed, not trifid; ovary with 2 apical tufts of glandular trichomes;
seeds with branched hygroscopic trichomes; widespread..............
....................................................................................... Blepharis
14 Seeds glabrous or sericeous-puberulous; stigma bilobed; bracts
terminating in a single spine; plants often robust, ± tall perennial
herbs, shrubs or small trees; widespread ........................Acanthus
14 Seeds covered in long hygroscopic trichomes; stigma 1-lobed;
bracts terminating in 3 or 5 simple or compound spines; plants of-
ten compact shrublets or acaulescent perennial herbs, if taller then
slender; SW Africa .................................................... Acanthopsis
Key to the genera of Barlerieae
1 Calyx 4-lobed, anterior lobe entire or bifid for less than half its
length; anterior and posterior lobes typically larger and broader
than lateral lobes and often enclosing them; corolla limb variously
arranged, lobes subregular or in a 4 + 1 or 2 + 3 configuration,
without hooded upper lip; staminal filaments ?always twisted
and crossing near the base ................................................Barleria
1 Calyx 5-lobed, if lobes unequal then lateral lobes not enclosed;
if calyx 4-partite with largely fused anterior lobes then corolla
strongly bilabiate with hooded upper lip; stamens not twisted and
crossing near the base .................................................................. 2
2 Androecium of 4 stamens, didynamous, with or without 1 stam-
inode.. ............................................ ............................................. 3
2 Androecium of 2 stamens, usually with 2 or 3 staminodes ....... 14
3 All anthers bithecous ................................................................... 4
3 Anthers of longer pair of stamens bithecous, those of shorter pair
of stamens monothecous............................................................ 12
4 Stamens included within corolla tube; stigma flattened, fan-shaped
or rhombic; corolla weakly bilabiate, posterior pair of lobes par-
tially fused but not for ming a hooded upper lip .......................... 5
4 Longer pair of stamens exserted from corolla tube or clearly visi-
ble at corolla mouth; stigma capitate-bilobed; corolla strongly bila-
biate, posterior pair of lobes largely or wholly fused to form
a ± hooded upper lip.................................................................. 10
5 Flowers in often large spherical heads with several whorls of
bracts, outermost bracts with a spiny or bristly margin and/or large,
20 mm long or more; continental Africa ......................... Crabbea
5 Flowers arranged in smaller, non-spherical heads or in spikes,
glomerules or panicles; bracts not spiny, smaller; Madagascar [7]
..................................................................................................... 6
6 Inflorescences pedunculate axillary heads, spikes, umbels or dicha-
sial panicles, or if fasciculate then inflorescence units held within
paired clasping bracts ........................................................................ 7
6 Inflorescences sessile, axillary glomerules, inflorescence units not
held within paired clasping bracts ............................................... 9
7 Flowers subtended by a whorl of (3) 4 bracts, these connate for at
least half their length to form a 3–4-lobed epicalyx; corolla 37–
50 mm long..................................................................... Boutonia
7 Flowers or inflorescence units subtended by a pair of bracts; bracts
not connate or only basally so; corolla up to 25 mm long ..............8
20 Version of Record
Manzitto-Tripp & al. •Revised classification and keys to Acanthaceae TAXON 00 (00) •1–51

8 Inflorescences of spikes, dichasial panicles or heads; pairs of
bracts subtending each inflorescence unit often unequal, not ad-
pressed, variously shaped ..................................... Podorungia [8]
8 Inflorescences of umbels (sometimes fasciculate) or lax dichasia;
pairs of bracts subtending each inflorescence unit subequal, ad-
pressed, ovate or elliptic ..................................... Pseudodicliptera
9 All bracts of glomerules linear or lanceolate, without recurved api-
ces; plants often with dense pale indumentum on stems and/or ab-
axial surface of leaves.................................................Lasiocladus
9 Outermost bracts of glomerules broader, foliaceous, sometimes
with recurved apices; plants without dense pale indumentum.......
.....................................................................................Pericalypta
10 Anther thecae conspicuously spurred at base; China to Malaysia
................................................................................. Chroesthes
10 Anther thecae not spurred at base, either obtuse or at most mi-
nutely apiculate .......................................................................... 11
11 Capsule stipitate; seeds glabrous; calyx lobes homomorphic; bracts
and bracteoles small and inconspicuous; Borneo..... Borneacanthus
11 Capsule not or barely stipitate; seeds with hygroscopic trichomes;
calyx lobes ± markedly heteromorphic, posterior lobe broadest,
lateral lobes narrowest; bracts and bracteoles usually conspicuous,
often similar to calyx lobes in shape and size; widespread ...........
.................................................................................. Lepidagathis
12 Plants spiny with axillary spines and/or spinose leaf margins;
Caribbean.......................................................................Barleriola
12 Plants without axillary spines or spinose leaf margins .............. 13
13 Stamens exserted beyond corolla lobes; corolla limb very short and
not strongly bilabiate (although posterior pair of lobes is fused); in-
florescence a many-flowered thyrse with flowers in dense whorls at
each node; bracts and bracteoles inconspicuous; New Guinea......
............................................................................. Hulemacanthus
13 Stamens not exserted beyond corolla lobes; corolla limb strongly
bilabiate; inflorescence a secund spike, spikes sometimes com-
pounded into dense heads; bracts and bracteoles usually conspicu-
ous; widespread ........................................................ Lepidagathis
14 Calyx lobes unequal, posterior lobe clearly broadest (2 + 2 + 1
configuration); seeds covered in long hygroscopic trichomes;
inflorescences markedly secund; widespread ....... Lepidagathis
14 Calyx lobes subequal, all linear; seeds with minute trichomes to-
wards the rim only; inflorescence a congested spiciform thyrse,
not secund; D.R. Congo ......................................... Schaueriopsis
Key to the genera of Andrographideae
1 Filaments swollen (pouched) distally; corolla subequally 5-lobed,
not clearly bilabiate...................................................................... 2
1 Filaments not swollen or pouched; corolla bilabiate or subequally
5-lobed......................................................................................... 3
2 Cladodes (reduced abortive branches) present in the inflorescence, ter-
minated by paired small spines; seeds not compressed, with 2 distinct
grooves, surface with hygroscopic tr ichomes ...............Haplanthodes
2 Cladodes absent in inflorescence; seeds somewhat compressed,
not distinctly g rooved, surface lacking trichomes, verrucose ........
.............................................................................. Haplanthus [9]
3 Ovules 2 per locule; anthers glabrous, dehiscent by longitudinal
slit in central half or 2/3 of each theca........ Sphinctacanthus [10]
3 Ovules 3 or more per locule, or if 2 then anthers conspicuously
penicillate at base and dehiscent by longitudinal slit in distal half
extending to apex ......................................................................... 4
4 Capsule compressed perpendicular to the septum, elliptic, oblan-
ceolate or narrowly oblong in face view; seeds subglobose, ellip-
soid or block-like, not compressed, often pitted or rugose and
grooved; anthers often penicillate at base ........ Andrographis [11]
4 Capsule not compressed, narrow throughout and 4-angled; seeds
markedly compressed, smooth and lacking trichomes, or covered
in trichomes; anthers not penicillate ............................................ 5
5 Calyx 4-lobed; slender procumbent herbs ................. Graphandra
5 Calyx 5-lobed; habit variable but not procumbent herbs............. 6
6 Staminodes present ........................................ Phlogacanthus [12]
6 Staminodes absent ....................................................................... 7
7 Corolla tube shorter than limb; upper lip ± curved.... Diotacanthus
7 Corolla tube longer than limb; upper lip not curved......................
..............................................................................Gymnostachyum
Key to the genera of Whitfieldieae
1 Seeds covered in hygroscopic trichomes that obscure the seed sur-
face; androecium of 2 stamens and (usually) 2 staminodes; corolla
salverform (or sinus between the anterior pair of lobes broader than
the other sinuses), tube narrowly cylindrical throughout...............
....................................................................................Lankesteria
1 Seeds lacking trichomes, surface with concentric rings at least to-
wards rim; androecium of 4 stamens (very rarely reduced to 2 stam-
ens plus 2 staminodes in occasional flowers); corolla form various
but not salverform with tube narrowly cylindrical throughout........ 2
2 Flowers in well-developed racemes or spikes, these sometimes
branched to form panicles; tropical Africa and Madagascar ....... 3
2 Flowers in axillary or subterminal fascicles, glomerules or short
umbels; Madagascar [13]............................................................. 4
3 Each inflorescence unit 1-flowered; calyx ≥9 mm long, usually ex-
tending beyond or subequal in length to bracteoles, often showy
and can be colored similar to corolla...........................Whitfieldia
3 Each inflorescence unit either 1-flowered or 2–3-flowered; calyx
up to 8 mm long, hidden within paired bracteoles, not colored sim-
ilar to corolla.....................................................Chlamydacanthus
4 Peduncle of each inflorescence unit conspicuous, filiform, 7–14 mm
long, considerably longer than bracteoles and calyces .. ..Zygoruellia
4 Inflorescence units either sessile or peduncles shorter than or equal
in length to bracteoles and calyces, not filiform.......................... 5
5 Corolla bright orange-red or scarlet, tube markedly curved; sta-
mens exserted well beyond corolla lobes..................... Camarotea
5 Corolla variously colored but not bright orange-red or scarlet, tube
straight or curved; stamens not or only slightly exserted beyond
corolla lobes ................................................................................. 6
6 Corolla tube subequal in length to limb, limb strongly bilabiate,
lobes of upper lip partially fused, all lobes with long wispy white
trichomes internally .............................................Leandriella [14]
6 Corolla tube longer than limb, often markedly so, limb not strongly
bilabiate, lobes of upper lip more deeply divided, or limb sube-
qually 5-lobed, all lobes lacking long white trichomes internally
.......................................................... Forcipella/Vindasia [15]
Key to the genera of Ruellieae
1 Filament curtain lacking .............................................................. 2
1 Filament curtain present .............................................................. 5
2 Anther filament connective tissue positioned lateral to thecae,
thecae facing outward in a 180° configuration from connective
tissue ........................................................................................3
2 Anther filament connective tissue positioned dorsal to thecae, the-
cae held parallel (i.e., side-by-side) as typical in Acanthaceae.... 4
3 Plants with basal rosettes of leaves ..............................Pararuellia
3 Plants upright, with cauline leaves.................................................
......................................................“Pseudosiphonium ined.”[16]
4 Plants with long, tubular flowers (≥5 cm total length), these yellow
to white, narrow, unexpanded portions of tubes ≥2× longer than ex-
panded portions; leaves not in a basal rosette; Papuasia................
.............................................................................Leptosiphonium
4 Plants with short, infundibuliform flowers (<5 cm total length),
these mostly purple, narrow unexpanded portions of tubes ± equal
to expanded portions (or marginally different in length, not as
above); leaves typically held in a basal rosette; Australia, New
Caledonia, New Guinea ............................................. Brunoniella
5 Pollen with coarse reticulate exine; corolla with a very long, nar-
row, unexpanded portion of tube; androecium of 2 stamens + 2 sta-
minodes; ovary with 4 ovules...................................................... 6
Version of Record 21
TAXON 00 (00) •1–51 Manzitto-Tripp & al. •Revised classification and keys to Acanthaceae

5 Pollen, corolla, androecium, and ovule number various, but not in
the above combination ................................................................. 7
6 Dichasia of 2 flowers typically arranged in terminal spikes, each
flower subtended by a single leaf-like bract; pollen colporate; tropical
Asia ................................................................................ Eranthemum
6 Dichasia typically of 2 flowers, axillary and not arranged into ter-
minal spikes, each flower subtended by pair of leaf-like bracts; pol-
len porate; west-central Africa................................. Kosmosiphon
7 All anther thecae lacking basal awns or appendages ................... 8
7 One or more anther thecae with basal awns or appendages....... 27
8 Corolla with a rugula and with rows of trichomes on the inner sur-
face of posterior corolla; transverse fusion of f ilaments creating a
ridge or “strobilanthoid”type of filament curtain ....................... 9
8 Corolla lacking a rugula or rows of trichomes; filament curtain not
“strobilanthoid”......................................................................... 10
9 Ovaries with ≤4 ovules ............................................ Strobilanthes
9 Ovaries with >4 ovules .......................................Strobilanthes s.l.
[incl. Hemigraphis/Clarkeasia/Stenosiphonium] [17]
10 Androecium of 2 stamens + 2 staminodes................................. 11
10 Androecium of 4 stamens .......................................................... 14
11 Ovaries with 2 ovules; pollen with sexine lips, 12-pseudocolpate;
plants usually strongly odoriferous with a creosote-like smell ......
.................................................................................... Duosperma
11 Ovaries with >2 ovules; pollen lacking sexine lips and not 12-
pseudocolpate; plants not typically strongly odoriferous .......... 12
12 Corolla very large, gullet-shaped, pale green to greenish-yellow
(sometimes with maroon tinges), cream-colored, or entirely dark
maroon; primarily nocturnal, and adapted to bat pollinators; calyx
3-lobed; pollen lacking pseudocolpi..........................Louteridium
12 Corolla various but not in the above character combination, and
rarely yellow; calyx not 3-lobed; pollen with 4 pseudocolpi......13
13 Plants usually large herbs to large shrubs; corolla strongly bilabi-
ate, hooded; leaf bases decurrent onto the petiole and forming a
wing; plants typically of forests and woodlands or their margins ....
...................................................................................... Brillantaisia
13 Plants typically small herbs; corolla usually more weakly bilabi-
ate, typically not hooded; leaf bases not typically decurrent onto
the petiole thus not forming a wing; plants typically of riparian
corridors ......................................................................Hygrophila
14 Plants with large, inflated calyces with calyx lobes fused nearly to
the apex (thus appearing tubular); all plant surfaces covered with
large, prominent glands ............................................ Satanocrater
14 Plants lacking large, inflated, nearly completely fused calyces;
plant surfaces with or without glands but not to the extent and size
as above ..................................................................................... 15
15 Corolla with all 5 lobes comprising the lower lip (thus 1-lipped)....
............................................................................Eremomastax [18]
15 Corolla not 1-lipped ................................................................... 16
16 Corolla with conspicuous “herring-bone”pattern characterizing
lower throat and/or lip surfaces; transverse folds of corolla forming
an additional fold (in addition to transverse fusion of filaments),
or “corolla fold”type of filament curtain; corolla typically strongly
bilabiate but weakly bilabiate in a few species .......................... 17
16 Corolla lacking “herring-bone”patterning; filament curtain not of
the “corolla fold”type; corolla typically rotate to zygomorphic,
only distinctly bilabiate in a few species ................................... 18
17 Large herbs typically >1 m in height; leaves drying blackish in
color; pollen grains 2-aperturate........................Calacanthus [19]
17 Small herbs typically <1 m in height; leaves not drying blackish in
color; pollen grains 4-aperturate..................................Hygrophila
18 Calyx 3-lobed ............................................................ Louteridium
18 Calyx not 3-lobed ...................................................................... 19
19 Corolla with flattened, apically rounded, uni- or bicellular tri-
chomes lining inner corolla surfaces; pollen spherical, echinate,
lacking ring of echinae surrounding the apertures.......Acanthopale
19 Corolla lacking trichomes as described above; pollen various but
not spherical, echinate, and lacking the ring of echinae ............ 20
20 Ovary with 2 ovules; pollen with sexine lips and 12-pseudocol-
pate; plants usually strongly odoriferous with a creosote-like smell
.................................................................................... Duosperma
20 Ovary with >2 ovules (rarely reduced to 2); pollen lacking sexine
lips and not 12-pseudocolpate; plants not typically strongly odor-
iferous.........................................................................................21
21 Calyx conspicuously zygomorphic............................................ 22
21 Calyx typically actinomorphic or at most weakly zygomorphic......
.......................................................................................................23
22 Calyx with 3 anterior lobes fused to varying degrees, 2 posterior
lobes mostly free; dorsalmost lobe lacking conspicuous marginal
veins; pollen spherical, echinate, and with conspicuous ring of
echinae sur rounding the apertures .................. Dischistocalyx [20]
22 Calyx in a 2 + 2 + 1 configuration with dorsalmost lobe the larg-
est, the 2 ventral lobes intermediate in size, the 2 lateral lobes the
smallest, and all lobes free to the receptacle; dorsalmost lobe with
conspicuous marginal veins; pollen spherical, coarsely reticulate,
ring of echinae absent........................................... Dinteracanthus
23 Shrubs or trees to 25 m tall and usually >4 m in height at maturity;
plants often used as fence posts; restricted to southern Central
America and northern South America ......................Trichanthera
23 Herbs, shrubs, or treelets, but clearly not true trees; plants not used
as fenceposts to our knowledge; widespread ............................. 24
24 Plants covered in dense tomentum of golden-yellow pubescence;
pollen bicolporate with numerous bands of pseudocolpi oriented
perpendicular to opposing face........................... Trichosanchezia
24 Plants not as above; pollen not as above....................................25
25 Pollen spherical, exine coarsely reticulate, lacking pseudocolpi and
lacking sexine lips ............................................................. Ruellia
25 Pollen 3-porate, 12-pseudocolpate, pores flanked by sexine lips .... 26
26 Capsule with fracturing placentae ............................... Phaulopsis
26 Capsule remaining intact post-dehiscence, lacking fracturing
placentae.................................................................Heteradelphia
27 Plants creeping or trailing herbs characterized most frequently by
near linear leaves, giving overall gestalt a “grass-like”appearance
(rarely elliptical to obovate); restricted to Namib and Kalahari
Deserts ......................................................................... Ruelliopsis
27 Plant habit various but not creeping with linear leaves and “grass-
like”in appearance; widespread ................................................ 28
28 Capsule with fracturing placentae ............................................. 29
28 Capsule with placentae that remain attached to capsular wall at
time of dehiscence ..................................................................... 30
29 Flowers lacking pair of conspicuously leaf-like bracts; pollen
grains with sexine lips ................................................. Phaulopsis
29 Conspicuous pair of relatively large, leaf-like bracts subtending
each flower; pollen grains with 4 areas of raised tectum, triangular
in polar view.................................................................Petalidium
30 Anther thecae each with 2 appendages................... Diceratotheca
30 Anther thecae otherwise ............................................................ 31
31 Pollen polypseudocolpate with 40+ pseudocolpi..............................
................................................................“Sinoacanthus ined.”[21]
31 Pollen otherwise ........................................................................ 32
32 Calyx lobes fused for at least 1/3 of their length and usually
over half of their length, with hyaline regions bordering each
lobe ............................................................................................ 33
32 Calyx lobes unfused or variously fused but rarely over 1/3 of their
length, lacking hyaline regions bordering each lobe ................. 34
33 Ovary with 4 ovules, capsule with (up to) 4 seeds ........................
............................................................................ Dyschoriste [22]
33 Ovary with 8 ovules, capsule with more than 4 seeds...................
.............................................................................. Echinacanthus
34 Leaves conspicuously dentate or crenate ................................... 35
34 Leaves entire or weakly dentate to crenate, but not conspicu-
ously so ...................................................................................... 36
35 Outermost theca of each of longer pair of stamens with a conspic-
uous appendage, other thecae with much shorter appendages or
rounded................................................................Mimulopsis [23]
22 Version of Record
Manzitto-Tripp & al. •Revised classification and keys to Acanthaceae TAXON 00 (00) •1–51

35 Either both thecae or one of each pair of thecae of all anthers with
an appendage ............................................................. Mellera [24]
36 Plants with long tubular, bird-pollination adapted flowers, often
bright red, pink, orange, or yellow in color; pollen bicolporate with
numerous bands of pseudocolpi oriented perpendicular to oppos-
ing face ...................................................................................... 37
36 Plants with various flowers and pollen, but not as above .......... 38
37 Androecium of 2 stamens + 2 staminodes.................... Sanchezia
37 Androecium of 4 stamens ...................................... Suessenguthia
38 Capsules usually 2-seeded ......................................................... 39
38 Capsules with >2 seeds.............................................................. 40
39 Corolla bilabiate, 10–12.5 mm long, tube cylindrical, without a
clearly expanded throat; lower lip with long bristly trichomes inter-
nally; pollen with 12 pseudocolpi; SW Angola .............. Mcdadea
39 Corolla subactinomorphic, not strongly bilabiate, 22–45 mm
long, tube clearly differentiated into a narrow basal tube and
an expanded throat; pollen with 18+ pseudocolpi; Angola to
D.R. Congo and to Zimbabwe..........................Strobilanthopsis
40 Inflorescences of very long, terminal spikes, these commonly
30 cm in length; Malaysia ........................................ Stenothyrsus
40 Inflorescences variable, primarily of racemes, less commonly of
spikes or solitary flowers, but if a spike, these not so elongate, con-
sistently <15 cm long ................................................................ 41
41 Evergreen shrubs or trees, precocious flowering absent; ultimate
branches not as below; pollen bicolporate with numerous bands
of pseudocolpi oriented perpendicular to opposing face; Neo-
tropics...............................................................................Bravaisia
41 Deciduous tree to 5 m tall, flowering before the leaves appear
(precocious flowering); ultimate branches numerous and curved-
ascending; pollen not as above; karst hills of Laos .......................
........................................................................... Xylacanthus [25]
III. Geographical keys to the genera of Acanthaceae
Key to the genera of Acanthaceae in Africa,
Madagascar, the Mediterranean region,
and the Arabian Peninsula
1 Mangrove trees or shrubs with pneumatophores present; fruit a
leathery 1-seeded capsule .............................................. Avicennia
1 Herbs, shrubs, woody twiners or small trees, not mangrove trees,
without pneumatophores; fruit an explosively dehiscent capsule,
not leathery, with (1) 2 or more seeds, or a 1–2-seeded drupe .... 2
2 Seeds not borne on hook-shaped retinacula, retinacula lacking or
papilliform; plants without cystoliths; anthers bithecous............. 3
2 Seeds borne on prominent hook-shaped retinacula; plants with or
without cystoliths, if cystoliths absent then anthers monothecous
[8] .............................................................................................. 11
3 Herbs or shrubs, not twining; paired bracteoles present or absent
but not large and conspicuous; flowers usually alternate or spirally
arranged in few- to many-flowered inflorescences; calyx deeply 4-
or 5-lobed; fruit a many-seeded (usually >10 seeds), capsule, not
woody .......................................................................................... 4
3 Herbaceous twiners or lianas, less frequently free-standing shrubs
or herbs; flowers solitary or in fascicles or racemes of opposite
flowers, not spirally arranged; flowers subtended by conspicuous
clasping or partially connate paired bracteoles; calyx a subentire
or undulate rim or with irregular teeth, or obscurely 5-lobed; fruit
either a 1–2-seeded drupe or a 2–4-seeded woody capsule ......... 8
4 Peduncles bearing alternate clasping scale-like sterile bracts; all
bracts sclerophyllous; leaves held in rosettes or whorls ................
.........................................................................................Elytraria
4 Peduncles (if present) without clasping scale-like bracts; bracts
membranous or foliaceous; leaves opposite, at least some pairs dis-
persed along the stems ................................................................. 5
5 Bracteoles absent; inflorescence of dense ± cylindrical spikes with
imbricate bracts; calyx 4-lobed, the anterior lobe with bifid apex
(rarely more deeply divided into 5 lobes); stamens 2, staminodes
absent............................................................................... Nelsonia
5 Bracteoles present; inflorescence variable but if spikes cylindrical
then not so dense; calyx 5-lobed; stamens 4, adaxial staminode
often also present (rarely reduced to 2 stamens + 2–3 staminodes)
................... ................................. .................................... ........... 6
6 Pairs of bracteoles inserted below receptacle, not adnate (leaves
not ternate; corollas <3 cm long); lateral 2 lobes of calyx can be
somewhat shorter than other lobes but not markedly so and not hid-
den by the bracteoles; W and C Africa........................Staurogyne
6 Pairs of bracteoles partially adnate to receptacle and sometimes
base of calyx (or if bracteoles sometimes free in Anisosepalum le-
wallei, then leaves mostly ternate and corollas 3–4 cm long); lat-
eral 2 calyx lobes markedly shorter than other lobes and largely
hidden by the bracteoles .............................................................. 7
7 Plants delicate trailing herbs; petiole usually longer than leaf blade;
anther thecae with a basal appendage, this often forked; corolla
widened almost from the base into a campanulate throat, palate
of lower lip not bullate, i.e., without raised bosses; Gabon to
Tanzania, Madagascar .......................................... Saintpauliopsis
7 Plants erect or procumbent herbs or subshrubs; petiole usually
shorter than leaf blade; anther thecae with basal appendages ab-
sent or short, apiculate, not forked; corolla with a cylindrical basal
tube, and ± gradually widened throat, not appearing campanulate,
palate of lower lip bullate, i.e., with raised bosses; C and E
Africa ...................................................................... Anisosepalum
8 Fruit a fleshy drupe with 1 or 2 seeds.......................................... 9
8 Fruit a 2–4-seeded woody capsule............................................. 10
9 Drupe with 2 seeds, large (3–10 cm in diam.); leaves with a cha-
racteristic ± long narrow basal portion above an abruptly rounded
or cordate base, can appear as a winged petiole; Congo Rep.,
D.R. Congo........................................................... Anomacanthus
9 Drupe with a single seed, not so large; leaves without base as
above; widespread........................................................Mendoncia
10 Anthers opening by apical pores; seed with a scar on proximal
face; indumentum stellate, bracteoles with a dense orange, red or
mustard-yellow stellate indumentum covering external surface.....
.....................................................................................Pseudocalyx
10 Anthers opening by longitudinal slits; seed hollowed on proximal
face; indumentum usually not stellate, bracteoles without a very
dense orange, red or mustard-yellow indumentum externally.......
....................................................................................Thunbergia
11 Stamens 4, sometimes with an additional staminode ................ 12
11 Stamens 2, with or without additional staminodes .................... 61
12 Anthers all monothecous; plants without cystoliths .................. 13
12 Either anthers all bithecous or 2 anthers bithecous and 2 anthers
monothecous; plants with cystoliths .......................................... 21
13 Calyx long-tubular, cylindrical to inflated, with short lobes; cap-
sule with more than 4 seeds; corolla aestivation left-contort; W
and C Africa ........................................................... Physacanthus
13 Calyx not markedly tubular, deeply divided into 4 or 5 lobes;
capsule with up to 4 seeds; corolla aestivation not contorted .... 14
14 Corolla lobes not comprising a single lip, either regularly 5-lobed
or bilabiate; corolla not yellow ........................ Stenandriopsis [4]
14 Corolla limb comprising a single lip, entire or 3- or 5-lobed, held
either ventrally or dorsally, or at least with the sinus between the
2 uppermost (or outermost) lobes at a markedly wider angle than
that of the other lobe sinuses, if only weakly so then corollayellow
(Crossandra flava) ..................................................................... 15
15 Corolla tube twisted through 180°, the single corolla lip held dor-
sally, entire or 3-lobed; Tanzania.............................Streptosiphon
15 Corolla tube not twisted, corolla lip held ventrally, 3- or 5-lobed or
sometimes only undulate ........................................................... 16
16 Stamens included in corolla tube, subsessile, not inserted on a
thickened flange ........................................................................ 17
16 Stamens exserted from the corolla tube, with flattened bone-like
filaments, inserted on a thickened flange .................................. 18
Version of Record 23
TAXON 00 (00) •1–51 Manzitto-Tripp & al. •Revised classification and keys to Acanthaceae

17 Calyx 4-lobed, anterior lobe bifid; bracts not imbricate, smaller
than bracteoles, these conspicuous, elliptic or obovate, diverging
widely from inflorescence axis; corolla tube not narrowly cylindri-
cal, limb obscurely 5-lobed or erose; Liberia to Tanzania.............
................................................................................ Crossandrella
17 Calyx 5-lobed; bracts usually imbricate, larger than and enclosing
bracteoles, these linear to lanceolate, not diverging widely from in-
florescence axis; corolla tube narrowly cylindrical, limb 5-lobed;
widespread.................................................................. Crossandra
18 Calyx 5-lobed; seeds sculptured with pectinate scales or concen-
tric rings; bracts, bracteoles and calyx lobes glumaceous.............
..................................................................................Sclerochiton
18 Calyx 4-lobed; seeds covered in hygroscopic trichomes, puberu-
lous or glabrous, without scales or concentric rings; bracts, bracte-
oles and calyces rarely glumaceous ........................................... 19
19 Anterior pair of staminal filaments each with an obtuse or acute
tooth-like appendage towards the apex ventrally........... Blepharis
19 Anterior staminal filaments lacking appendages ....................... 20
20 Seeds glabrous or sericeous-puberulous; stigma bilobed; bracts
terminating in a single spine; plants often robust, ± tall perennial
herbs, shrubs or treelets; widespread ..............................Acanthus
20 Seeds covered in long hygroscopic trichomes; stigma 1-lobed;
bracts terminating in 3–5 simple or compound spines; plants often
compact shrublets or acaulescent perennial herbs, if taller then
slender; Namibia, western South Africa .................... Acanthopsis
21 Longer 2 stamens bithecous, shorter 2 stamens monothecous but
sometimes with vestigial second theca, or if rarely (in few Neura-
canthus) all stamens bithecous then shorter pair with anthers al-
most sessile and corolla with short tube and funnel-shaped limb
comprising equal anterior and lateral lobes and partially to almost
completely fused dorsal pair of lobes ........................................ 22
21 All stamens bithecous, filaments present; corolla not as above ....
................................................................................................... 24
22 Calyx bilabiate, with a 2-lobed or -toothed anterior lip and a
3-lobed or -toothed posterior lip; corolla with a funnel-shaped limb
comprising equal anterior and lateral lobes and partially (or almost
completely) fused dorsal pair of lobes, not bilabiate .....................
................................................................................ Neuracanthus
22 Calyx 5-lobed, lobes either equal or with posterior lobe widest
(2 + 2 + 1 configuration); corolla bilabiate ............................... 23
23 Bracts obovate with rounded apex, often with conspicuous darker
pinnate-anastomosing venation; calyx ± equally 5-lobed, mark-
edly shorter than bracteoles; small trailing herbs of rainforest;
Nigeria, Bioko, Cameroon..........................................Afrofittonia
23 Bracts variously shaped but apex acute to acuminate, 3- to pal-
mately veined or venation inconspicuous; calyx unequally 5-
lobed, posterior lobe clearly broadest (2 + 2 + 1 configuration),
not or only slightly shorter than bracteoles; habit and habitat vari-
ous but often in drier habitats; widespread ............... Lepidagathis
24 Calyx 4-lobed, anterior lobe entire or bifid for less than half its
length; anterior and posterior lobes typically much broader than
lateral lobes and often enclosing them; corolla variously arranged,
lobes subregular or in a 4 + 1 or 2 + 3 (rarely 1 + 3) configuration,
without a hooded upper lip; filaments of anterior (long) pair of sta-
mens ?always twisted and crossing near the base..................Barleria
24 Calyx (3-) 5-lobed, or if anterior pair of lobes partially fused and
lobes of unequal width then corolla markedly bilabiate with a
± hooded upper lip; staminal filaments not twisted and crossing
near the base .............................................................................. 25
25 Stamens in 2 pairs with filaments fused at base, sometimes form-
ing a filament curtain within the corolla tube............................ 26
25 Stamens not in 2 pairs, filaments not fused, f ilament curtain absent
................................................................................................... 49
26 Seeds usually tuberculate or rugose, often with a thickened and
irregularly crenate or serrate margin, more rarely smooth and
rounded, lacking trichomes; corolla bilabiate (sometimes weakly
so), with ascending-cochlear aestivation ................................... 27
26 Seeds with hygroscopic trichomes present throughout or at least
along the rim; or if (rarely) glabrous then corolla subactinomor-
phic; corolla with left-contort aestivation .................................. 29
27 Flowers solitary in leaf axils; Botswana, South Africa..................
.................................................................................. Glossochilus
27 Flowers held in well-developed spikes or racemes, sometimes
compounded into panicles ......................................................... 28
28 Anthers with thecae offset, rounded at the base; inflorescence a
slender racemose thyrse with opposite cymose units; west-central
Africa........................................................................... Filetia [26]
28 Anthers with thecae held at an equal or subequal height, usually
basally spurred or apiculate; inflorescence often a secund spike
or raceme, more rarely with opposite cymose units; widespread.....
....................................................................................Asystasia [27]
29 All anther thecae ± rounded at base, lacking basal appendages ....
................................................................................................... 30
29 One or both thecae of at least 2 of the 4 anthers with basal
appendages ................................................................................ 42
30 Calyx large, inflated, fused nearly to the apex with only short
lobes; all plant surfaces covered in large, prominent scale-like
glands; Guinea, NE Africa ....................................... Satanocrater
30 Calyx not large and inflated, not fused nearly to the apex; plant sur-
faces with or without glands but not covered in dense scale-like
glands.............................................................................................31
31 Corolla 1-lipped, with all 5 lobes comprising the lower lip (or
rarely lip held in upper position due to floral resupination resulting
from twisting of the tube) ........................................Eremomastax
31 Corolla not 1-lipped ................................................................... 32
32 Calyx with 3 posterior lobes fused for half their length or more,
2 anterior lobes free to the receptacle (2 + 3 conf iguration);
Guineo-Congolian forests .......................................................... 33
32 Calyx without 3 posterior lobes conspicuously fused ...............34
33 Pollen coarsely reticulate; corolla tube cylindrical, only narrowly
widened towards mouth, geniculate; W and C Africa ...................
............................................................. Ruellia [Endosiphon] [20]
33 Pollen echinate, not coarsely reticulate; corolla tube infundibuli-
form, not markedly geniculate; Nigeria to D.R. Congo.................
............................................................................... Dischistocalyx
34 Calyx strongly zygomorphic, posterior lobe conspicuously broader
than the other lobes, ovate, elliptic or rhombic, the other lobes
linear-lanceolate to oblanceolate, the 2 anterior lobes slightly bro-
ader than the 2 lateral lobes (2 + 2 + 1 configuration), all divided
± to the receptacle..........................................................................35
34 Calyx (sub)actinomorphic or if zygomorphic then not as above;
posterior lobe not markedly broader than other lobes ..................36
35 Capsule with fracturing placentae; flowers held in strobilate to
more lax spikes, usually dorsiventral, with flowers and fertile
bracts ventrally and sterile bracts dorsally, or rarely flowers solitary
and axillary; pollen prolate, 12(+)-pseudocolpate, exine finely re-
ticulate; widespread ..................................................... Phaulopsis
35 Capsule without fracturing placentae; inflorescences simple or
compound dichasia, not strobilate or dorsiventral; pollen spherical,
lacking pseudocolpi, exine coarsely reticulate; Angola, Namibia
...................................................................Dinteracanthus [28]
36 Capsule 2-seeded ....................................................................... 37
36 Capsule 4- to many-seeded........................................................ 38
37 Calyx divided almost to the receptacle into 5 subequal (posterior
sometimes longer) lobes; corolla with flattened, apically rounded,
uni- or bicellular trichomes lining inner surface, tube usually ±
markedly curved; stigma with 1 linear lobe, second lobe reduced
to a short tooth; plants without a creosote-like smell; widespread
...............................................................................Acanthopale
37 Calyx with fused basal portion and zygomorphic limb due to
partial fusion of anterior pair of lobes; corolla without such tri-
chomes internally, tube straight; stigma bilobed; plants usually
strongly odiferous with a creosote-like smell; E and S Africa,
Arabia ......................................................................... Duosperma
24 Version of Record
Manzitto-Tripp & al. •Revised classification and keys to Acanthaceae TAXON 00 (00) •1–51

38 Calyx lobes fused for at least 1/3 of their length and usually over
half their length, with marginal hyaline regions, lobes linear(-lan-
ceolate); capsule 4-seeded; stigma lobe with flat straight margin;
pollen prolate with 12+ pseudocolpi and with sexine lips around
the short apertures ...................................................... Dyschoriste
38 If calyx fused for over 1/3 of their length and with linear lobes and
capsule 4-seeded (some Ruellia in Madagascar), then calyx lack-
ing hyaline margins, stigma lobe with involute irregular margin
and pollen spheroid, coarsely reticulate, lacking pseudocolpi and
sexine lips .................................................................................. 39
39 Corolla typically strongly bilabiate with 2-lobed hooded upper lip
and 3-lobed lower lip often with conspicuous “herring-bone”pat-
terning, or if corolla only weakly bilabiate then less than 1 cm
long; plants of (seasonal) wetlands..............................Hygrophila
39 Corolla subactinomorphic or if zygomorphic then not strongly
bilabiate with hooded 2-lobed upper lip, lacking or with only faint
“herring-bone”patterning on lower lip; corolla usually >1 cm
long; plants not of wetlands....................................................... 40
40 Pollen spherical, exine coarsely reticulate or rarely (in our region
only known in Ruellia togoensis) with large verrucae, lacking
pseudocolpi or sexine lips; flowers usually axillary, solitary or in
fascicles, more rarely in lax axillary dichasia or (in R. dissidens
only) a slender terminal spike............................................ Ruellia
40 Pollen prolate, 3-porate and 12-pseudocolpate, pores flanked by
sexine lips; flowers held in a terminal thyrse or panicle ............ 41
41 Corolla limb either zygomorphic, with 1 lobe splitting from the
tube earlier than and considerably longer than the other 4
lobes, or if subactinomorphic then lobes narrowly oblong with
rounded apices and staminal filaments puberulous; Tanzania ......
................................................ Mimulopsis [Epiclastopelma] [29]
41 Corolla limb subactinomorphic, lobes elliptic or oblong with emar-
ginate apices; staminal filaments glabrous; Guinea to Ivory Coast,
São Tomé .................................................................Heteradelphia
42 Flowers subtended by a pair of conspicuous, ± large bracteoles,
these papery to leathery and often with conspicuous reticulate
venation, enclosing the calyx and base of the corolla; southern
Africa............................................................................Petalidium
42 Flowers not subtended by a pair of conspicuous bracteoles ...... 43
43 Capsules with fracturing placentae; calyx strongly zygomorphic,
posterior lobe ovate or elliptic, markedly broader than other lobes,
these linear-lanceolate to oblanceolate (2 + 2 + 1 configuration);
inflorescences often dorsiventral spikes, with flowers and fertile
bracts ventrally and differently shaped sterile bracts dorsally, rarely
radially symmetrical .................................................... Phaulopsis
43 Capsules without fracturing placentae or with placentae easily dis-
lodged but lateral walls of capsule not tearing; calyx actinomorphic
or only weakly zygomorphic, posterior lobe not markedly broader
than other lobes; inflorescences not dorsiventral spikes........44
44 Corolla limb subactinomorphic, throat lacking “herring-bone”pat-
terning; plants with trailing or procumbent stolons from a woody
rootstock sometimes rooting adventitiously, with clusters of leaves
or short erect leafy stems along the stolons, leaves linear to nar-
rowly elliptic or obovate, plant often with a “grass-like”gestalt;
southern Africa ............................................................ Ruelliopsis
44 Corolla limb zygomorphic or weakly so, throat often with promi-
nent “herring-bone”patterning; plant habit not as above, not
grass-like ................................................................................... 45
45 Calyx lobes fused for at least 1/3 of their length and usually over
half their length, with hyaline margins between the lobes, lobes
linear(-lanceolate); ovary with 2 ovules per locule, capsule
4-seeded...................................................................... Dyschoriste
45 Calyx lobes divided to the receptacle or shortly fused, lacking hy-
aline margins; lobes linear or often spathulate; ovary with 2–8
ovules per locule; capsule often either >4-seeded or 2-seeded...... 46
46 Outermost theca of each of longer pair of stamens with a conspic-
uous curved appendage, other thecae with much shorter append-
ages or rounded .......................................................... Mimulopsis
46 Either all thecae or 1 of each pair of thecae of all anthers with an
appendage.................................................................................. 47
47 Leaves conspicuously dentate or crenate; capsule with >4 and usu-
ally ≥8 seeds; seeds with hygroscopic trichomes largely restricted
to the rim, surfaces with or without short non-hygroscopic tri-
chomes; E and S Africa ............................................. Mellera [24]
47 Leaves entire or with a single tooth on each side; capsule usually
2-seeded, hygroscopic trichomes covering entire seed surface ....48
48 Corolla bilabiate, 10–12.5 mm long, tube cylindrical, without a
clearly expanded throat; lower lip with long bristly trichomes inter-
nally; pollen with 12 pseudocolpi; SW Angola .............. Mcdadea
48 Corolla subactinomorphic, not strongly bilabiate, 22–45 mm long,
tube clearly differentiated into a narrow basal tube and an expan-
ded throat; pollen with 18+ pseudocolpi; Angola to D.R. Congo
and Zimbabwe .....................................................Strobilanthopsis
49 Seeds (where known) sculptured with concentric rings at least towards
the rim, lacking trichomes; corolla with left-contort aestivation..... 50
49 Seeds not sculptured with concentric rings, either covered in tri-
chomes or, if glabrous, then surface smooth; corolla with quincun-
cial aestivation ........................................................................... 55
50 Flowers held in well-developed racemes or spikes, sometimes bran-
ched to form panicles; continental Africa and Madagascar .. ........... 51
50 Flowers held in axillary or subterminal fascicles, glomerules or
short umbels; Madagascar [13] ................................................. 52
51 Inflorescence units 1-flowered; calyx ≥9 mm long, usually extend-
ing beyond or subequal in length to bracteoles, often showy and
colored similar to corolla; widespread in tropical continental
Africa........................................................................... Whitfieldia
51 Inflorescence units 1- or 2–3-flowered; calyx short, up to 8 mm
long, hidden within paired bracteoles, not colored similar to co-
rolla; Kenya, Tanzania, Madagascar ................Chlamydacanthus
52 Peduncle of inflorescence units conspicuous, filiform, 7–14 mm
long, considerably longer than bracteoles and calyces ..................
.................................................................................... Zygoruellia
52 Inflorescence units either sessile or peduncles shorter than or equal
in length to bracteoles and calyces, not filiform........................ 53
53 Corolla bright orange-red or scarlet, tube markedly curved; sta-
mens exserted well beyond corolla lobes .................... Camarotea
53 Corolla variously colored but not bright orange-red or scarlet, tube
straight or curved; stamens not or barely exserted beyond corolla
lobes .......................................................................................... 54
54 Corolla tube subequal in length to limb, limb strongly bilabiate,
lobes of upper lip partially fused, all lobes with long wispy white
trichomes internally ............................................. Leandriella [14]
54 Corolla tube longer than limb, often markedly so, limb not so
strongly bilabiate, lobes of upper lip more deeply divided, or limb
subactinomorphic, all lobes lacking long white trichomes internally
.................................................................. Fo r c i pe l l a /Vindasia [15]
55 Longer pair of stamens exserted from corolla tube or clearly visible
at corolla mouth; stigma capitate-bilobed; corolla strongly bilabi-
ate with 2 posterior lobes largely or completely fused to form a
hooded upper lip ....................................................... Lepidagathis
55 Stamens included within corolla tube; stigma flattened, fan-shaped
or rhombic; corolla not so strongly bilabiate, posterior pair of lobes
fused somewhat higher than other lobes but not forming a hooded
upper lip ..................................................................................... 56
56 Flowers held in ± spherical heads surrounded by several whorls of
bracts, outermost bracts with a spiny or bristly margin and/or long,
≥20 mm long; E and S Africa.......................................... Crabbea
56 Flowers arranged in smaller, non-spheroidal heads or in spikes,
glomerules or panicles; bracts not spiny, smaller; Madagascar [7]
................................................................................................... 57
57 Inflorescences pedunculate axillary heads, spikes, umbels or di-
chasial panicles, or if fasciculate then inflorescence units held
within paired clasping bracts ..................................................... 58
57 Inflorescences sessile axillary glomerules, inflorescence units not
held within paired clasping bracts ............................................. 60
Version of Record 25
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58 Flowers subtended by a whorl of (3) 4 bracts connate for at least
half their length to form a 3–4-lobed epicalyx; corolla 37–50 mm
long................................................................................. Boutonia
58 Flowers or inflorescence units subtended by a pair of bracts;
bracts not connate or only basally so; corolla up to 25 mm long
............................................................................................. 59
59 Inflorescences of spikes, dichasial panicles or heads; bracts sub-
tending each inflorescence unit paired but the pairs often unequal,
not adpressed, variously shaped ................................. Podorungia
59 Inflorescences of umbels (sometimes fasciculate) or lax dichasia;
bracts subtending each inflorescence unit paired, subequal, ad-
pressed, ovate or elliptic ..................................... Pseudodicliptera
60 All bracts of glomerules linear or lanceolate, without recurved api-
ces; plants often with dense pale indumentum on stems and/or ab-
axial surface of leaves.................................................Lasiocladus
60 Outermost bracts of glomerules broader, foliaceous, sometimes
with recurved apices; plants without dense pale indumentum ......
.....................................................................................Pericalypta
61 Anthers monothecous ................................................................ 62
61 Anthers bithecous ...................................................................... 67
62 Corolla resupinate through ±180° twist in corolla tube; flowers
held between paired clasping or partially fused ± conspicuous
bracts .............................................................................Hypoestes
62 Corolla not resupinate, tube not twisted; pairs of bracts neither
clasping nor partially fused ....................................................... 63
63 Corolla either subregularly 5-lobed or if bilabiate then upper lip con-
spicuously 2-lobed and lower lip deeply divided into 3 lobes; stami-
nodes 2, sometimes basally fused to filaments of fertile stamens;
seeds either smooth on both faces, or smooth on outer face and irreg-
ularly ridged on inner face, this with or without a raised rim .........64
63 Corolla strongly bilabiate, upper lip undivided or at most shortly
notched, lower lip only partially divided into 3 lobes or almost
undivided; staminodes absent; seeds tuberculate, rugulose or with
concentric ridges, without a raised rim...................................... 66
64 Corolla tube much longer than limb, markedly curved and gradu-
ally expanded towards mouth; Socotra .......................... Ballochia
64 Corolla tube either shorter than limb or if longer than limb then
narrowly cylindrical throughout except for slight expansion at
the mouth; not on Socotra ......................................................... 65
65 Corolla tube narrowly cylindrical, longer than limb; limb either
subequally 5-lobed or bilabiate with posterior 2 lobes partially
fused, anterior 3 corolla lobes not reflexed or widely divergent....
................................................................................. Ruspolia [30]
65 Corolla tube more broadly cylindrical or saccate, shorter than or
subequal to limb; posterior pair of lobes partially fused and erect,
anterior 3 corolla lobes either reflexed and held against the tube,
or widely divergent ............................................................. Ruttya
66 Corolla with tube up to 10 mm long, upper lip lanceolate, hooded,
largely enclosing the staminal filaments (flower nototribic); C and
E Africa ...........................................................Monothecium [31]
66 Corolla with tube longer than 10 mm or, if shorter, then upper lip
subulate, oblong-lanceolate or elliptic, not hooded, often recurved
or inrolled, stamens held between the 2 lips (flower pleurotribic);
widespread......................................................... Brachystephanus
67 Staminodes present, sometimes basally fused to the adjacent stam-
inal f ilament............................................................................... 68
67 Staminodes absent ..................................................................... 81
68 Calyx 4-lobed, anterior lobe entire or bifid for less than half its
length; anterior and posterior lobes typically much broader than
lateral lobes and often enclosing them; corolla arrangement vari-
able, lobes subregular or in a 4 + 1 or 2 + 3 configuration, without
hooded upper lip; staminal filaments ?always twisted and crossing
near the base .....................................................................Barleria
68 Calyx 5-lobed or equally 4-lobed, or if anterior pair of lobes par-
tially fused (less than half their length) and lobes of unequal width
then corolla markedly bilabiate with ± hooded upper lip; staminal
filaments not twisted and crossing near the base ...................... 69
69 Pollen bipororate, circular in apertural view, with a broad marginal
girdle-like ring of sexine; flowers held in axillary and subterminal
glomerules on largely leafless woody stems; corolla with dense tuft
of yellow trichomes on palate of lower lip immediately proximal to
the lobes; Madagascar ............................................... Ritonia [32]
69 Pollen and macromorphological characters not in the above
combination ............................................................................... 70
70 Seeds with hygroscopic trichomes present throughout or at least
around the rim; corolla either with left-contort or quincuncial
aestivation.................................................................................. 71
70 Seeds without hygroscopic trichomes, sculptured with tuberculae,
echinae or verruculae, or smooth; corolla with ascending-cochlear
aestivation.................................................................................. 78
71 Corolla salverform, with narrowly cylindrical tube markedly longer
than spreading 5-lobed limb; limb subactinomorphic or with sinus
between 2 adaxial lobes wider than the other sinuses ................ 72
71 Corolla not salverform, often markedly bilabiate or, if limb sub-
actinomorphic, then tube not long and narrowly cylindrical......
............................................................................................. 73
72 Corolla blue or violet; flowers held in (1)2(3)-flowered dichasia in
the axils of leaves, each flower subtended by a pair of conspicuous
ovate foliaceous bracteoles held on a winged pedicel; Cameroon,
Central African Republic, D.R. Congo ................... Kosmosiphon
72 Corolla yellow, orange or white; flowers held in terminal spikes or
dense thyrses, often with conspicuous imbricate bracts, or bracts
linear; bracteoles linear; winged pedicels absent; widespread.......
....................................................................................Lankesteria
73 Filament curtain absent; corolla aestivation quincuncial ........... 74
73 Filament curtain present; corolla aestivation left-contort .......... 75
74 Inflorescences dense secund spikes with unequal fertile and ster-
ile bracts; calyx lobes markedly unequal in 2 + 2 + 1 configuration,
posterior lobe broadest, ovate or elliptic; seeds with long hygroscopic
trichomes; Madagascar [33]............................................ Lepidagathis
74 Inflorescences dense terminal thyrses, not secund, pairs of bracts
equal; calyx of 5 subregular linear lobes; seeds with minute tri-
chomes only; D.R. Congo ...................................... Schaueriopsis
75 Capsule 2-seeded; 2 anterior calyx lobes fused more distally than 3
posterior lobes, inflorescences not subtended by spines................
.................................................................................... Duosperma
75 Capsule 4- to ca. 30-seeded; anterior calyx lobes not fused more
distally than posterior lobes or, if so, then fascicles of flowers sub-
tended by hard spines ................................................................ 76
76 Leaf base decurrent onto petiole, forming a ± marked wing; corolla
strongly bilabiate with laterally compressed and curved hooded
upper lip and basally hinged lower lip........................... Brillantaisia
76 Leaf base not winged; corolla not so strongly bilabiate, upper lip
may be hooded but not laterally compressed nor so strongly cur-
ved, lower lip not basally hinged ............................................... 77
77 Capsule 4-seeded; lower corolla lip lacking stiff retrorse bristles;
anther thecae usually spurred; plants usually of dry habitats ........
.................................................................................... Dyschoriste
77 Capsule 8–20+-seeded; lower lip of corolla with numerous stiff
retrorse bristles; anther thecae not spurred; plants of (seasonal)
wetlands.......................................................................Hygrophila
78 Inflorescence of curved secund spikes, with the flowers held
upright, 1 flower per inflorescence node; corolla tube markedly
infundibuliform, with basal cylindrical portion and abruptly wid-
ened throat; South Africa, Eswatini................................ Mackaya
78 Inflorescences of axillary solitary flowers or fascicles, or of slen-
der spikes with opposite flowers or fascicles at each inflorescence
node; corolla tube cylindrical throughout or, if with an expanded
throat, then throat gradually widened ........................................ 79
79 Corolla tube curved and gradually widened distally, 7–10 mm in
diam. at mouth; dorsal pair of corolla lobes largely fused to form
hooded upper lip; Nigeria, Bioko, Cameroon ...... Graptophyllum
79 Corolla tube cylindrical to narrowly so or at most narrowly campa-
nulate, up to 3 mm in diam. at mouth, straight or ± abruptly bent
26 Version of Record
Manzitto-Tripp & al. •Revised classification and keys to Acanthaceae TAXON 00 (00) •1–51

distally; dorsal pair of corolla lobes not largely fused, upper lip not
hooded ....................................................................................... 80
80 Inflorescences long slender spikes; corolla tube usually much lon-
ger than limb, rarely shorter than limb; widespread ......................
.........................................................................Pseuderanthemum
80 Inflorescence axillary (but branches can be largely leafless at flow-
ering), flowers solitary or in fascicles; corolla tube shorter than
limb; Madagascar ..................................................... Oplonia [34]
81 Corolla resupinate through ±180° twist in corolla tube ............. 82
81 Corolla not resupinate or if so, then due to twisting of pedicel, co-
rolla tube not twisted ................................................................. 84
82 Thecae of each anther widely separated by extension of the con-
nective tissue; Madagascar ......................................... Vavara [35]
82 Anther thecae immediately superposed or slightly overlapping ....
................................................................................................... 83
83 Capsule with fracturing placentae, placenta base and thin walls
tearing away from thickened flanks ............................... Dicliptera
83 Capsule without fracturing placentae, walls and placenta base re-
maining attached at dehiscence ........................ [Peristrophe] [36]
84 Corolla strongly bilabiate with lips markedly longer than tube (of-
ten 2× longer or more), upper lip strongly hooded, straight to grad-
ually curved, lower lip narrowly oblong, strap-shaped or narrowly
cylindrical, usually recoiled at anthesis ..................................... 85
84 Corolla limb various, if bilabiate, then lips usually not markedly
longer than tube or if so then lower lip broader and not recoiled
at anthesis .................................................................................. 87
85 Pollen bipororate, circular in apertural view, with a broad marginal
girdle-like ring of sexine (“gürtelpollen”); inflorescence spikes
slender with rachis sometimes visible between the pairs of bracts;
Madagascar.............................................. Anisotes perplexus [37]
85 Pollen 2-, 3- or 4-colporate with pseudocolpi flanking each aper-
ture, prolate, without a marginal girdle; inflorescences variable but
if spikes then more contracted with usually imbricate bracts, not
so slender .......................................................................................86
86 Capsule with fracturing placentae; Nigeria, E and S Africa ..........
............................................................................ Metarungia [38]
86 Capsule without fracturing placentae; widespread .......... Anisotes
87 Flowers sternotribic; trailing or procumbent herb with axillary fas-
cicles of flowers; bracts, bracteoles and calyx lobes with pale-
hyaline margins; Kenya .......................................... Kenyacanthus
87 Plants without the above combination of characters.................. 88
88 Pollen bipororate, circular in apertural view, with a broad marginal
girdle-like ring of sexine (“gürtelpollen”); corolla bilabiate; an-
thers with thecae either held at an equal height and parallel or offset
to fully superposed and/or oblique, basally muticous, if offset then
the upper theca slightly longer than the lower theca .....................
................. Isoglossa/Melittacanthus/Sphacanthus/Celerina [39]
88 Pollen variable but not as above; if anther thecae offset to super-
posed then often with a basal appendage on the lower theca or both
thecae, and the upper theca slightly shorter than the lower theca
............................................................................................. 89
89 Anther thecae each with a broad flattened appendage with irregular
projections along the rim (resembling a “chicken’s crest”); corolla
intricately speckled or striped, lacking a rugula; Nigeria, Bioko,
Cameroon, Gabon................................................... Champluviera
89 Anther thecae either without appendages or if appendages present
then not as above, appendages apiculate to well-developed and
elongate, often curved, sometimes with a bif id apex but without
projections along the rim; corolla coloring various; if anther ap-
pendages present, then corolla with a rugula ............................. 90
90 Corolla lacking a rugula; anther thecae held at an equal height (but
sometimes unequal in size) and parallel or sagittate; anther ap-
pendages absent ......................................................................... 91
90 Corolla with a rugula present on upper lip and dorsal side of tube;
anther thecae usually strongly offset to fully superposed and/or
oblique; lower theca or both thecae often with a well-developed
appendage................................................................................ 101
91 Corolla 9–12 mm long, with narrowly cylindrical tube longer than
the limb; corolla lobes all reflexed at anthesis;anther thecae held at
± equal height but 1 theca larger than the other; pollen 6-colporate,
sculptured with verruculae arranged in ± well-defined longitudinal
lines; W and C Africa..........................................Chlamydocardia
91 If corolla with narrowly cylindrical tube then considerably longer
than 12 mm; corolla lobes not all reflexed at anthesis but apices
can be recurved or recoiled; anther thecae not unequal in size; pol-
len not as above ......................................................................... 92
92 Upper lip of corolla curved and laterally compressed, very narrow;
lower lip lacking raised “herring-bone”pattern; seeds covered in
glochidiate tubercles; D.R. Congo, Kenya, Mozambique .............
...................................................................................Cephalophis
92 Plant not with the above combination of characters; if upper lip of
corolla curved and laterally compressed then lower lip with con-
spicuous raised “herring-bone”pattern and seeds not covered in
glochidiate tubercles .................................................................. 93
93 Upper lip of corolla not hooded, sometimes apically recurved or
recoiled; lower lip without raised “herring-bone”pattern; seeds
discoid with a raised rim............................................................ 94
93 Upper lip of corolla ± hooded; lower lip often with raised “herring-
bone”pattern; seeds less strongly flattened, without a marginal
rim ........................................................................................... 100
94 Inflorescences pendulous; corolla ascending-sigmoid-shaped in
bud, tube strongly expanded apically; lower lip shortly 3-lobed;
Socotra.................................................................... Angkalanthus
94 Inflorescences erect; corolla not ascending-sigmoid-shaped in
bud, tube cylindrical or only slightly widened upwards; lower lip
deeply 3-lobed ........................................................................... 95
95 Upper corolla lip broadly elliptic with rounded or slightly emar-
ginate apex; leaves lanceolate with length: width ratio 7–9: 1, lon-
gest leaves 11–15 cm long; Madagascar .......................................
.............................................................................. Dolichostachys
95 Upper corolla lip linear-lanceolate to narrowly elliptic, apex acute
or notched; leaves variable, if narrow then less than 10 cm long
............................................................................................. 96
96 Corolla tube narrowly cylindrical, barely widened at mouth, often
longer than lobes; upper lip markedly smaller than lower lip; sta-
mens held close to upper lip of corolla with short f ilaments (flower
nototribic), anthers parallel to filament ..................Ecbolium [40]
96 Corolla tube cylindrical to somewhat campanulate but not nar-
rowly cylindrical, shorter than or subequal in length to lobes; upper
lip ± equal in length to lower lip; stamens held ± equidistant be-
tween the upper and lower lips (flower pleurotribic), anthers often
held per pendicular to filaments ................................................. 97
97 Corolla lobes spreading or recurved but not recoiled at anthesis;
pollen 3-colporate with only weakly defined colpi and lacking
pseudocolpi; E and S Africa, Arabian Peninsula...........................
............................................................................. Megalochlamys
97 Corolla lobes, at least on lower lip, becoming apically recoiled at
anthesis; pollen 3–6-colporate, colpi conspicuous, pseudocolpi
present ....................................................................................... 98
98 Inflorescence 4-angular with imbricate slightly concave bracts;
pollen (4) 5 (6)-colporate, with pseudocolpi fused towards one or
both poles to form arcs, circles or ellipses; coastal Kenya and
Tanzania ...................................................................... Trichaulax
98 Inflorescence not conspicuously 4-angular, if bracts imbricate then
convex; pollen 3-colporate, pseudocolpi not fused towards poles,
parallel to the colpi .................................................................... 99
99 Plants from Madagascar .......................................... Populina [41]
99 Plants from Socotra, Somalia, Botswana, South Africa ................
.................................................................................Chorisochora
100 Calyx zygomorphic (2 + 2 + 1 configuration), lobes oblong-ellip-
tic to oblong-oblanceolate, posterior lobe broadest, 4–7 mm wide;
Madagascar .................................................................. Ambongia
100 Calyx not or barely zygomorphic, lobes linear or lanceolate, less
than 4 mm wide; Ethiopia, Somalia ........................ Ichthyostoma
Version of Record 27
TAXON 00 (00) •1–51 Manzitto-Tripp & al. •Revised classification and keys to Acanthaceae

101 Corolla tube narrowly cylindrical throughout or ventrally abruptly
expanded in distal half, usually considerably longer than lips
except in R. pulcher where lower lip >20 mm long; upper lip
linear-lanceolate to shortly ovate, not hooded; anthers with the-
cae muticous or lower theca apiculate ................. Rhinacanthus
101 Corolla tube not so narrowly cylindrical throughout nor abruptly
expanded on ventral side of tube, if tube longer than lips then up-
per lip hooded; anthers usually with well-developed basal
appendages ......................................................................... 102
102 Capsule with fracturing placentae; inflorescences strobilate se-
cund spikes, bracts often with conspicuous and abrupt white- or
pinkish hyaline margins .......................................................... 103
102 Capsule with placentae not fracturing; inflorescences variable, if
strobilate, secund spikes then bracts without abrupt pale hyaline
margins (margins sometimes gradually paler) ......................... 104
103 Anthers dehiscing by basal pores; Nigeria, Cameroon, Equatorial
Guinea, Gabon ............................................................. Ascotheca
103 Anthers dehiscing by longitudinal slits; widespread ......... Rungia
104 Capsule 2-seeded (rarely 4-seeded), seeds smooth, glabrous or
white-sericeous, or with 2 tufts of moniliform trichomes .......105
104 Capsule usually 4-seeded, more rarely 2-seeded, seeds variously
sculptured or with short trichomes, rarely smooth .................. 106
105 Inflorescences of axillary or both axillary and terminal spikes;
bracts elliptic, ovate or obovate, often imbricate, inflorescence
units at each axil often >1-flowered; seeds 2–3 mm in diam., lenti-
cular with a sharp rim, ± symmetrical in cross section and lacking
a prominent ridge on one side, glabrous ........... Meiosperma [42]
105 Inflorescences either axillary and 1-flowered (bracts undifferen-
tiated from the leaves) or in well-defined, mostly terminal spikes
(bracts highly modified), rarely in axillary pedunculate fascicles;
bracts in species with well-defined spikes usually narrow, linear
to lanceolate, or rarely (in one species) broadly elliptic to obovate;
seeds variable, often larger than 3 mm in diam. with a rounded rim
(including in the single species with broad bracts) and/or variously
pubescent, or if small and with sharp rim then asymmetric in cross
section and with a prominent ridge on one side............................
............................................................................Pogonospermum
106 Corolla red or orange with tube somewhat curved and gradually
widened, longer than lips; anthers with both thecae appendaged;
Socotra .......................................................................Trichocalyx
106 Corolla variable but usually with ± straight tube; if corolla red and
with curved, gradually widened tube, then anthers with only the
lower theca appendaged .......................................................... 107
107 Inflorescences secund spikes with usually imbricate, obovate, spa-
thulate or lanceolate bracts, these green, white or pink; seeds sub-
globose, with hygroscopic or papillose trichomes; mainly Mada-
gascar, 1 sp. widespread in tropical Africa.............. Anisostachya
107 Inflorescences variable; if secund spikes with imbricate bracts
then seeds not as above, primarily without (rarely with) hygro-
scopic or papillose trichomes; widespread ................ Justicia [43]
Key to the genera of Acanthaceae in Asia
and Australasia (excluding the Arabian
Peninsula and Mediterranean region)
1 Mangrove trees or shrubs with pneumatophores present; fruit a
leathery 1-seeded capsule .............................................. Avicennia
1 Herbs, shrubs, woody twiners, or small trees, not mangrove trees
(although occasionally mangrove shrubs in Acanthus), without
pneumatophores; fruit a woody or thin-walled capsule with (1) 2
or more seeds ............................................................................... 2
2 Seeds not borne on hook-shaped retinacula, either retinacula lack-
ing or papilliform; plants without cystoliths; all anthers bithecous
..................................................................................................... 3
2 Seeds borne on prominent hook-shaped retinacula; plants with
or without cystoliths, if cystoliths absent then anthers mono-
thecous.................................................................................... 7
3 Herbs or shrubs, not twining; paired bracteoles present or absent
but not large and conspicuous; calyx deeply 4- or 5-lobed; fruit a
many-seeded (usually >10 seeds) capsule ................................... 4
3 Herbaceous twiners or lianas, less frequently free-standing shrubs
or herbs; flowers solitary or in fascicles or racemes of opposite
flowers, not spirally arranged; calyx a subentire or undulate rim
or with irregular teeth, or obscurely 5-lobed; fruit a 2–4-seeded
capsule ......................................................................................... 6
4 Peduncles bearing spirally arranged, clasping, scale-like sterile
bracts; all bracts sclerophyllous; leaves held in rosettes or basal
whorls; India, Sri Lanka ..................................................Elytraria
4 Peduncles (if present) without clasping scale-like bracts; bracts
membranous or foliaceous; leaves mostly opposite, at least some
pairs dispersed along the stems.................................................... 5
5 Stamens 2, staminodes absent; bracteoles absent (rarely present);
inflorescence of dense ± cylindrical spikes with imbricate bracts;
calyx 4-lobed, the anterior lobe with bif id apex (rarely more deeply
divided into 5 lobes) ........................................................Nelsonia
5 Stamens 4, adaxial staminode often also present, or rarely reduced
to 2 stamens +2–3 staminodes; bracteoles present; inflorescence
variable but, if spikes cylindrical, then not so dense; calyx
5-lobed.........................................................................Staurogyne
6 Stigma ± equally 2-lobed, each lobe subdivided into 2 unequal
lobes; pollen 7–9-lobate and -colpate; India .................... Meyenia
6 Stigma funnel-shaped, unequally 2-lobed or if equally so then not
subdivided; pollen spiraperturate and unlobed; widespread..........
....................................................................................Thunbergia
7 Stamens 4, sometimes with an additional staminode................... 8
7 Stamens 2, with or without additional staminodes .................... 39
8 Anthers all monothecous; plants without cystoliths; corolla
1-lipped........................................................................................ 9
8 Either anthers all bithecous or 2 anthers bithecous and 2 anthers
monothecous; plants with cystoliths; arrangement of corolla lobes
various but not 1-lipped............................................................. 12
9 Stamens included in corolla tube, subsessile, not inserted on a thick-
ened flange; India and Sri Lanka to Myanmar.............. Crossandra
9 Stamens exserted from corolla tube, with flattened bone-like fila-
ments, inserted on a thickened flange........................................ 10
10 Anterior staminal filaments lacking appendages, if flattened then
gradually narrowed towards apex; seeds glabrous or sericeous-
puberulous ......................................................................Acanthus
10 Anterior pair of staminal filaments flattened and either with an ob-
tuse or acute tooth-like appendage or truncate to rounded towards
apex ventrally; seeds with branched hygroscopic trichomes or
tuberculate ................................................................................. 11
11 Leaves opposite; flowers solitary or paired in the leaf axils, each
flower or pair of flowers subtended by 2 pairs of bracts, outer
pair entire, inner pair trifid; ovary without apical tufts of glandular
trichomes; seeds tuberculate; India .....................Cynarospermum
11 Leaves in pseudowhorls of (3) 4; inflorescences variable but not
consisting of solitary or paired flowers in leaf axils; bracts entire
or toothed, not trifid; ovary with 2 apical tufts of glandular tri-
chomes; seeds with branched hygroscopic trichomes; widespread
....................................................................................... Blepharis
12 Calyx distinctly bilabiate, with a 2-lobed or -toothed anterior lip
and a 3-lobed or -toothed posterior lip; corolla with a funnel-
shaped limb comprising equal anterior and lateral lobes and par-
tially (or almost completely) fused dorsal pair of lobes; India to
Laos ........................................................................ Neuracanthus
12 Calyx not distinctly bilabiate (although can appear so in Barleria),
either 4- or 5-lobed, lobes can be equal or unequal in shape and
size; if calyx appears bilabiate then corolla not as above..............
................................................................................................... 13
13 Calyx 4-lobed, anterior lobe entire or bifid for less than half its
length; anterior and posterior lobes typically much broader than
lateral lobes and often enclosing them; corolla variously arranged,
lobes subregular or in a 4 + 1 or 2 + 3 configuration, without hooded
28 Version of Record
Manzitto-Tripp & al. •Revised classification and keys to Acanthaceae TAXON 00 (00) •1–51

upper lip; filaments of anterior (long) pair of stamens ?always
twisted and crossing near the base........................................ Barleria
13 Calyx 5-lobed, or if anterior pairof lobes partially fused and lobes of
unequal width then corolla strongly bilabiate with ± hooded upper
lip; staminal filaments not twisted and crossing near the base.... 14
14 Seed surfaces smooth or sculptured, lacking trichomes; corolla
aestivation ascending-cochlear .................................................. 15
14 Seed surfaces either covered by trichomes or with trichomes at
least along margins and/or near the apices (trichomes minute in a
few genera, such as Hulemacanthus, absent in Borneacanthus);
corolla aestivation left-contort or quincuncial ........................... 19
15 One pair of stamens with bithecous anthers, the other pair with
monothecous anthers; Thailand, Malaysia............ Thysanostigma
15 Both pairs of stamens with bithecous anthers ........................... 16
16 Corolla strongly bilabiate with upper two lobes almost completely
fused into a hooded or erect, apically notched lip; either stamens
included in corolla tube or if exserted then anthers usually with
thecae unevenly inserted on the filament and offset by ca. half their
length ......................................................................................... 17
16 Corolla not so strongly bilabiate, 5 lobes often subequal although
arranged in a 2 + 3 configuration and upper two lobes can be par-
tially fused; stamens exserted, anther thecae held at a subequal
height ......................................................................................... 18
17 Mouth of corolla closed due to raised, rounded palate of lower lip,
upper lip held erect; stamens included in corolla tube, filaments
very short, anthers with thecae held at a subequal height; calyx
lobes apically reflexed; Borneo ................................. Linariantha
17 Mouth of corolla not closed, palate of lower lip can be raised but
not so strongly bulging, upper lip hooded, not erect; stamens ex-
serted and held within hooded upper lip, filaments well developed;
calyx lobes not markedly reflexed apically; Malaysia, Sumatra,
Borneo ......................................................................... Filetia [44]
18 Calyx with a ± distinct tubular portion, the tube sometimes longer
than the lobes; inflorescences often with opposite cymose units,
pedicels widely divergent from inflorescence axis and can be
thickened; India, Malaysia.............................. Phialacanthus [45]
18 Calyx divided ± to the base; inflorescences often secund, pedicels
not so widely diverging from the axis and not thickened;
widespread...................................................................... Asystasia
19 Corolla lacking a f ilament curtain ............................................. 20
19 Corolla with a conspicuous filament curtain ............................. 27
20 One pair of stamens with bithecous anthers, the other pair with
monothecous anthers ................................................................. 21
20 Both pairs of stamens with bithecous anthers ........................... 22
21 Stamens exserted beyond corolla lobes, corolla limb very short
and not strongly bilabiate (although posterior pair of lobes are par-
tially fused); inflorescence a many-flowered thyrse with flowers in
dense whorls at each node, not secund; bracts and bracteoles
inconspicuous; New Guinea ................................ Hulemacanthus
21 Stamens not exserted beyond corolla lobes, corolla limb strongly
bilabiate; inflorescence a secund spike, spikes sometimes com-
pounded into dense heads; bracts and bracteoles usually conspicu-
ous; widespread ........................................................ Lepidagathis
22 Corolla bilabiate, with ± hooded upper lip; corolla aestivation
quincuncial ................................................................................ 23
22 Corolla subactinomorphic or weakly zygomorphic, not strongly
bilabiate with hooded upper lip; corolla aestivation left-
contort .................................................................................25
23 Anther thecae conspicuously spurred at base; China to Malaysia
................................................................................. Chroesthes
23 Anther thecae not spurred at base, either obtuse or at most minut-
ely apiculate ............................................................................... 24
24 Capsule stipitate; seeds glabrous; calyx lobes all linear or linear-
lanceolate; bracts and bracteoles small and inconspicuous; Borneo
.............................................................................. Borneacanthus
24 Capsule not or barely stipitate; seeds with hygroscopic trichomes;
calyx lobes ± markedly unequal, posterior lobe broadest, lateral
lobes narrowest (2 + 2 + 1 configuration); bracts and bracteoles
usually conspicuous, often similar to calyx lobes in shape and size;
widespread................................................................ Lepidagathis
25 Flowers with “X-shaped anthers”(i.e., thecae extend outwardly in
a 180° configuration from expanded filament connective tissue);
China ...........................................................................Pararuellia
25 Anthers various but not “X-shaped”as above........................... 26
26 Plants with long-tubed, pale-colored corollas; leaves not held in a
basal rosette; Papuasia.........................................Leptosiphonium
26 Corollas not long-tubed and pale-colored, typically short infundi-
buliform, primarily purple; leaves typically held in a basal rosette;
Australia, New Caledonia, New Guinea.................... Brunoniella
27 Corolla strongly bilabiate .......................................................... 28
27 Corolla infundibuliform, campanulate or other shapes, not strongly
bilabiate ....................................................................................... 29
28 Plants large herbs or weak shrubs to 2.5 m tall; capsule oblong or
obovate, not with noticeably thin walls; ovules 4 or fewer per
ovary; India................................................................Calacanthus
28 Plants herbaceous, typically <1 m tall (very rarely to 1.5 m tall);
capsule cylindrical, with noticeably thin walls; ovules >8 per ovary,
capsule typically polyspermous (≥16 seeds); widespread ................
.........................................................................................Hygrophila
29 Capsule with fracturing placentae ............................................. 30
29 Capsules with non-fracturing placentae..................................... 31
30 Inflorescences complex, densely bracteate and compact, with nu-
merous, small flowers; flowers not subtended by large, conspicu-
ous, paired leaf-like bracts; corolla small (<10 mm long); anther
thecae without appendages; widespread ...................... Phaulopsis
30 Inflorescences axillary, solitary or in simple dichasia, not complex
and dense as above; flowers subtended by a large, conspicuous,
pair of leaf-like bracts; corolla >34 mm long; anther thecae with
appendages; India and Nepal........................................Petalidium
31 Anthers with at least some thecae with basal appendages ......... 32
31 Anthers lacking basal appendages ............................................. 36
32 Deciduous tree to 5 m tall, flowering before the leaves appear;
ultimate branches numerous and curved-ascending; karst hills of
Laos ................................................................... Xylacanthus [25]
32 Herbs or shrubs, habit not as above........................................... 33
33 Leaf pairs strongly and consistently anisophyllous, the smaller leaf
about 1/3 of the size of the larger; each anther theca with a pair of
appendages; Thailand ............................................. Diceratotheca
33 Leaf pairs sometimes slightly dissimilar in size but not strongly
(nor consistently) anisophyllous; anther thecae variously appen-
daged but not with 2 appendages per theca ............................... 34
34 Inflorescences of very long, terminal spikes, these commonly
30 cm in length; Malaysia ........................................ Stenothyrsus
34 Inflorescences variable, primarily of racemes, less commonly of
spikes or solitary flowers, if spikes, consistently <15 cm long ..... 35
35 Ovary with 8 ovules; India, China........................ Echinacanthus
35 Ovary with 4 ovules (occasionally fewer); widespread..............
.............................................................................. Dyschoriste
36 Ovary with 16 ovules........................................Strobilanthes [46]
36 Ovary primarily with fewer than 16 ovules (with rare exceptions)
................................................................................................... 37
37 Corolla resupinate via twisting of the tube through 180°; inflores-
cences thyrsoid with secondary flowers in the axils of bracteoles;
corolla with a ventricose throat .........................Strobilanthes [47]
37 Corolla usually not resupinate via twisting of the tube (except in
Strobilanthes dyeriana,S. autapomorpha,andS. steenisiana), but
corolla distortions sometimes achieved by bending of the corolla
throat; if resupinate, then not in combination with above additional
features...........................................................................................38
38 Corolla internally with prominent rows of trichomes along poste-
rior surface, these functioning to retain the style (very rarely sec-
ondarily lost); corolla typically with thin but prominent ridge
between pairs of stamens, representing vestigial staminode..........
................................................................................. Strobilanthes
Version of Record 29
TAXON 00 (00) •1–51 Manzitto-Tripp & al. •Revised classification and keys to Acanthaceae

38 Corolla internally lacking prominent rows of trichomes along
posterior surface; corolla lacking a ridge between pairs of
stamens........................................................................... Ruellia
39 Anthers monothecous ................................................................ 40
39 Anthers bithecous (one theca sometimes reduced in size) ........ 43
40 Corolla tube twisted through 180°, limb resupinate with the
3-lobed lower lip held in the upper position and unlobed or emar-
ginate upper lip held in the lower position; India to China and
Thailand.........................................................................Hypoestes
40 Corolla tube not twisted; if flower resupinate then this achieved
through geniculation of corolla tube.......................................... 41
41 Corolla 30–60 mm long, bright red-orange; clambering shrubs;
China to Indonesia................................................... Clinacanthus
41 Corolla up to 10 mm long, white or pale blue, with or without
red or mauve markings; perennial herbs or small shrubs, not
clambering ................................................................................. 42
42 Corolla with 4-lobed upper lip and unlobed lower lip; each anther
with theca terminal and transverse, sometimes also with a vestigial
second theca observed as a bump below the fertile theca; flowers
axillary and solitary, held on lateral branches; Australia...............
....................................................................... Xerothamnella [48]
42 Corolla with shortly bilobed, hooded upper lip and 3-lobed lower
lip; each anther with theca dorsifixed and ± parallel to filament,
without a vestigial second theca; inflorescence a small, dense se-
cund spike; India, Sri Lanka ................................... Monothecium
43 Staminal filament divided at apex, the thecae separated widely
by an elongate connective perpendicular to the f ilament; corolla
subactinomorphic with 5 ± equal lobes; Australia ........................
............................................................................... Dicladanthera
43 Stamens not as above, if thecae widely separated then vertically
offset to superposed; arrangement of corolla lobes various, but co-
rolla usually ± zygomorphic ...................................................... 44
44 Staminodes present, either free or basally fused to the adjacent
staminal f ilament ....................................................................... 45
44 Staminodes absent ..................................................................... 59
45 Calyx 4-lobed, anterior lobe entire or bifid for less than half its
length, anterior and posterior lobes typically much broader than
lateral lobes and often enclosing them; corolla arrangement vari-
able, lobes subregular or in a 4 + 1 or 2 + 3 configuration, without
a hooded upper lip; staminal filaments ?always twisted and cross-
ing near the base...............................................................Barleria
45 Calyx 5-lobed, or if anterior pair of lobes largely fused then corolla
markedly bilabiate with ± hooded upper lip; staminal filaments not
twisted and crossing near the base............................................. 46
46 Seeds with hygroscopic trichomes present throughout or at least
around the rim; corolla either with left-contort or quincuncial
aestivation.................................................................................. 47
46 Seeds without hygroscopic trichomes, variously tuberculate, echi-
nate, verruculate, puberulous, tomentellous or smooth; corolla
with ascending-cochlear aestivation .......................................... 51
47 Filament curtain absent; corolla with quincuncial aestivation; in-
florescences dense secund spikes that can be compounded into
complex heads, often with dimorphic fertile and sterile bracts; ca-
lyx lobes highly unequal, posterior lobe broadest, lateral lobes nar-
rowest (2 + 2 + 1 conf iguration) ..............................Lepidagathis
47 Filament curtain present; corolla with left-contort aestivation; in-
florescences variable but not dense secund spikes with dimorphic
bracts; calyx lobes (sub)equal to somewhat unequal, not in 2 + 2
+ 1 conf iguration....................................................................... 48
48 Corolla tube much longer than lobes, tube either narrowly cylindri-
cal throughout (corolla salverform) or with long cylindrical basal
portion and gradually expanded throat; inflorescences a series of
spikes, bracts often imbricate and often with conspicuous reticu-
late patterning ...........................................................Eranthemum
48 Corolla without such a long basal cylindrical tube, not salverform;
inflorescences not as above ....................................................... 49
49 Corolla internally with prominent rows of trichomes along
posterior surface, these functioning to retain the style; corolla typ-
ically with thin but prominent ridge between pair of stamens.......
................................................................................. Strobilanthes
49 Style not held in place by trichomes on corolla tube; corolla with-
out a prominent ridge between pair of stamens ......................... 50
50 Ovary with 4 ovules; lower corolla lip lacking stiff retrorse bristles;
anther thecae usually spurred; plants usually of dry ground .........
.................................................................................... Dyschoriste
50 Ovary with 8–20+ ovules; lower lip of corolla with numerous stiff
retrorse bristles; anther thecae not spurred; plants of (seasonal)
wetlands.......................................................................Hygrophila
51 Ovary with 8 or more ovules, capsule 8–16-seeded; pollen with ap-
erture margins conspicuously thickened and intricately ornamen-
ted with conical spines .................................. Phlogacanthus [12]
51 Ovary with 2 or 4 ovules; capsule 2- or 4-seeded; pollen without
thickened and ornamented aperture margins ............................. 52
52 Leaves strongly anisophyllous (appearing alternate), larger leaf of
a pair 9.5–19 × 2.5–6.7 cm, smaller leaf of a pair reduced to a
minute lanceolate blade 4–6×1–2 mm; Borneo...........................
............................................................ Ptyssiglottis staminodifera
52 Leaves isophyllous or not so markedly anisophyllous .............. 53
53 Corolla salverform, tube longer than limb and narrowly cylindrical
throughout or only slightly widened distally, limb either sube-
qually 5-lobed or only weakly bilabiate, if the posterior pair of
lobes partially fused then not forming a hooded upper lip ............
.................................................................Pseuderanthemum [49]
53 Corolla not salverform, if tube longer than limb and cylindrical,
then limb markedly bilabiate with posterior pair of lobes largely
fused and sometimes forming a hooded upper lip ..................... 54
54 Corolla small, up to 15 mm long but often ≤10 mm long ......... 55
54 Corolla much larger, >25 mm long ........................................... 58
55 Leaves with toothed, spinose or sinuate margin; inflorescences ax-
illary, 1-flowered or simple dichasia or fascicles; Australia, New
Guinea, Fiji....................................................Graptophyllum [50]
55 Leaves with ± entire margin; inflorescences spikes or racemes, of-
ten terminal.........................................................................56 [51]
56 Corolla campanulate, limb only weakly bilabiate; tube shorter than
limb and widened almost from the base; India to Japan and
Vietnam ............................................................... Codonacanthus
56 Corolla strongly bilabiate; tube longer than or subequal to limb,
not widened from the base......................................................... 57
57 Anther thecae basally muticous; corolla tube sometimes with a
dorsal pouch distally; China to Borneo ............. Cosmianthemum
57 Anther thecae with paired basal spurs; corolla tube without a
dorsal pouch; China................................................ Wuacanthus
58 Corolla tube markedly infundibuliform, with basal cylindrical por-
tion and abruptly widened throat; limb only weakly bilabiate, the 5
lobes subequal, upper lip not strongly hooded; corolla white or
rose-colored, with intricate darker veins; India, Bhutan, Myanmar,
China.....................................................................................Mackaya
58 Corolla tube more gradually widened from base to apex and
± strongly curved; limb bilabiate with posterior pair of lobes
forming a hooded upper lip; corolla red or bright pink; Australia,
New Guinea, Pacific Is., naturalized elsewhere ...... Graptophyllum
59 Corolla resupinate through ±180° twist in corolla tube; flowers
held between paired clasping bracts .......................................... 60
59 Corolla not resupinate or, if so, then due to twisting of pedicel,
corolla tube not twisted; flowers not held between paired clasping
bracts ......................................................................................... 61
60 Capsule with fracturing placentae; anther thecae rounded or
elliptic ............................................................................Dicliptera
60 Capsule without fracturing placentae; anther thecae (in Asia)
typically linear-oblong, rarely rounded or elliptic.............................
.............................................................................. [Peri st rophe] [36]
61 Anthers with thecae superposed and held patent to one another; co-
rolla with a conspicuously 2-lobed upper lip, each lobe forked;
Australia ........................................................ Xerothamnella [52]
30 Version of Record
Manzitto-Tripp & al. •Revised classification and keys to Acanthaceae TAXON 00 (00) •1–51

61 If anthers superposed and oblique then corolla with a shortly
2-lobed or emarginate upper lip, the lobes not forked............... 62
62 Pollen disc-shaped, bipororate with a broad marginal girdle of sex-
ine [53]; anthers with thecae ± markedly offset to fully superposed
and often highly oblique, sometimes 1 or both thecae perpendicu-
lar to f ilament, lacking basal appendages; rugula absent ..............
........................................................................................ Isoglossa
62 Pollen very variable but never disc-shaped with a marginal girdle;
anthers with thecae variously held at an equal height to strongly
offset, if offset then often with the lower theca or both thecae with
a basal appendage, and rugula present ...................................... 63
63 Rugula absent; anther thecae held at the same height or only slightly
offset, parallel to each other and to the filament or slightly sagittate;
thecae without appendages or with short uncurved appendages....64
63 Rugula present; anther thecae usually offset by at least half their
length or fully superposed, sometimes markedly oblique; lower
theca or more rarely both thecae often with a conspicuous ± curved
appendage, this typically pale.................................................... 79
64 Ovary with 6 or more ovules, capsule 6- to many-seeded, or if 2
ovules per locule and capsule 4-seeded then anthers penicillate at
base or thecae only dehiscing via a short slit in central half to
2/3; pollen with aperture margins and/or aperture surface conspi-
cuously thickened and often intricately ornamented with conical
spines ......................................................................................... 65
64 Ovary with 2 or 4 ovules; capsule 2- or 4-seeded; anthers not peni-
cillate at base, thecae dehiscing along± their full length; pollen with-
out thickened and ornamented aperture margins or surfaces ....... 72
65 Filaments swollen (pouched) distally; corolla subequally 5-lobed,
not clearly bilabiate ................................................................... 66
65 Filaments not swollen or pouched; corolla bilabiate or subequally
5-lobed....................................................................................... 67
66 Cladodes (reduced abortive branches) present in the inflorescence,
terminated by paired small spines; seeds not compressed, with 2
distinct grooves, surface with hygroscopic trichomes; India .........
................................................................................ Haplanthodes
66 Cladodes absent in inflorescence; seeds somewhat compressed,
not distinctly grooved, surface without trichomes, verrucose; wide-
spread ................................................................... Haplanthus [9]
67 Ovary with 4 ovules; anthers glabrous, dehiscent via longitudinal
slit in central half or 2/3 of each theca; India, Myanmar...............
.................................................................... Sphinctacanthus [10]
67 Ovary with 6 or more ovules, or if 4 then anthers conspicuously
penicillate at base and dehiscent via longitudinal slit in distal half
extending to apex....................................................................... 68
68 Capsule linear and 4-angled, not compressed; seeds markedly
compressed, smooth, can be covered in trichomes; anthers not
penicillate .................................................................................. 69
68 Capsule compressed perpendicular to the septum, elliptic, oblanceo-
late or narrowly oblong in face view; seeds subglobose, ellipsoid or
block-like, not compressed, often pitted or rugose and grooved; an-
thers often penicillate at base.........................................................71
69 Calyx 4-lobed; slender procumbent herbs; Thailand....... Graphandra
69 Calyx 5-lobed; habit variable but not procumbent herbs........... 70
70 Corolla tube shorter than limb; upper lip ± curved; India .............
................................................................................. Diotacanthus
70 Corolla tube longer than limb; upper lip not curved; widespread
........................................................................ Gymnostachyum
71 Capsule 6–20-seeded; India and Sri Lanka to Myanmar, intro-
duced elsewhere.......................................................Andrographis
71 Capsule 4-seeded; India, Sri Lanka ............... [Indoneesiella] [11]
72 Corolla blue-green or livid-green, tube narrowly cylindrical through-
out with only very short expanded throat, usually longer than limb,
upper lip linear-lanceolate, much smaller than lower lip; India and
Sri Lanka to Myanmar ........................................................ Ecbolium
72 Corolla variously colored but not shades of green, tube variously
shaped but if longer than limb then more gradually expanded and
lips not so unequal ..................................................................... 73
73 Inflorescences often on leafless portion of branches or on mature
woody stems (ramiflorous or cauliflorous), in fascicles or short
spikes; shrubs or small trees ...................................................... 74
73 Inflorescences either terminal or axillary on leafy portion of bran-
ches; herbs or shrubs ................................................................. 75
74 Corolla lips conspicuously longer than tube; lower lip strap-
shaped with 3 short rounded apical lobes; New Guinea..............
........................................................................... Calycacanthus
74 Corolla tube longer than lips; lower lip deeply divided into 3 linear-
lanceolate lobes; Vietnam........................................ Cyclacanthus
75 Calyx lobes lanceolate, with 3 or more parallel veins prominent at
maturity; corolla with ± markedly saccate throat above short basal
cylindrical tube .......................................................................... 76
75 Calyx lobes linear to linear-lanceolate, usually only the midrib pro-
minent or veins inconspicuous; corolla without markedly saccate
throat.......................................................................................... 77
76 Inflorescences1-flowered, these sometimes clusteredtowards branch
tips; anther thecae pubescent; pollen 3-colporate, 6-pseudocolpate;
Thailand .............................................................................. Marcania
76 Flowers held in branched thyrses; thecae glabrous; pollen 5-colporate,
10-pseudocolpate; New Guinea ...................................... Jadunia [54]
77 Inflorescences axillary, varying from lax dichasia to reduced and
contracted dichasia with 2(–4) contracted branches that can bear
several to many pairs of imbricate, scale-like bracts, or sometimes
reduced to single flowers; inflorescences not spiciform; Sri Lanka
to New Guinea............................................................ Ptyssiglottis
77 Inflorescences terminal, spiciform or, if branched, then branches
spiciform.................................................................................... 78
78 Corolla with strongly curved and hooded upper lip, upper lip either
shortly 2-lobed or 4-lobed, lower lip 3-lobed or 1-lobed; inflores-
cence often branched with branches spiciform, or sometimes un-
branched; India and China to Indonesia ...................Leptostachya
78 Corolla with a ± straight and not conspicuously hooded upper lip,
upper lip shortly 2-lobed, lower lip 3-lobed; inflorescence spici-
form, unbranched; Taiwan..............................Kudoacanthus [55]
79 Corolla tube narrowly cylindrical, considerably longer than lips;
upper lip lanceolate or narrowly so, not hooded; anthers with the-
cae lacking appendages; widespread ...................... Rhinacanthus
79 Corolla tube not so narrowly cylindrical, if tube longer than lips
then upper lip hooded; anther thecae with or (rarely) without basal
appendages, often with a conspicuous curved pale appendage on
the lower theca........................................................................... 80
80 Capsule with fracturing placentae; inflorescences usually secund
spikes with imbricate bracts; bracts with or without conspicuous
white or pinkish hyaline margins....................................... Rungia
80 Capsule without fracturing placentae; inflorescences variable, if
secund spikes with imbricate bracts then bracts without abrupt pale
hyaline margins ......................................................................... 81
81 Capsule 2-seeded, seeds smooth, discoid; India ........ Meiosperma
81 Capsule usually 4-seeded, seeds variously sculptured or rarely
smooth; widespread ................................................... Justicia [43]
Key to the genera of Acanthaceae in the Americas
1 Mangrove trees or shrubs with pneumatophores present; fruit a
leathery 1-seeded capsule .............................................. Avicennia
1 Herbs, shrubs, lianas or small trees, if (rarely) mangrove trees or
shrubs then pneumatophores lacking (can have aerial prop roots);
fruit either a ± woody or thin-walled capsule with 2 or more seeds,
or a 1-seeded drupe...................................................................... 2
2 Seeds not borne on hook-shaped retinacula, retinacula lacking or
papilliform; plants without cystoliths; all anthers bithecous......3
2 Seeds borne on prominent hook-shaped retinacula (retinacula in-
distinct in Aphanosperma and Chalarothyrsus, with seeds perma-
nently retained in capsule valves); plants with or without cystoliths,
if cystoliths absent then anthers mo nothecous...................... ........... 7
3 Herbaceous twiners or lianas; flowers subtended by conspicuous
clasping or partially connate paired bracteoles; calyx a subentire
Version of Record 31
TAXON 00 (00) •1–51 Manzitto-Tripp & al. •Revised classification and keys to Acanthaceae

or undulate rim or with irregular teeth, or obscurely 5-lobed; fruit a
1-seeded drupe ..................................................... Mendoncia [56]
3 Herbs or shrubs, not twining; paired bracteoles present or absent
but not large and conspicuous; calyx deeply 4- or 5-lobed; fruit a
many-seeded capsule (usually >10 seeds) ................................... 4
4 Peduncles bearing clasping scale-like sterile bracts; all bracts sclero-
phyllous; leaves in rosettes or whorls either basally or terminating
branches (sometimes dispersed along stems in E. imbricata and
E. mexicana) .......................................................................Elytraria
4 Peduncles (if present) without clasping scale-like sterile bracts;
bracts membranous or foliaceous; leaves opposite, at least some
pairs dispersed along the stems.................................................... 5
5 Bracteoles absent; inflorescence of dense ± cylindrical spikes with
imbricate bracts; calyx 4-lobed, the anterior lobe with bifid apex
(rarely more deeply divided into 5 lobes); stamens 2, staminodes
absent .......................................................................Nelsonia [57]
5 Bracteoles present; inflorescence variable but, if spikes cylindrical,
then relatively lax; calyx 5-lobed; stamens 4, adaxial staminode
often also present (rarely 2 stamens +2–3 staminodes) ............... 6
6 Plants subcaulescent (internodes indistinct or short); inflorescence
of axillary, long-pedunculate (peduncles 9.8–22 cm long) panicles
of spikes; ovary asymmetric with style arising on one side, stigma
1-lobed, subcapitate; Brazil ........................................ Aymoreana
6 Plants caulescent (internodes distinct, usually elongate); inflores-
cence of terminal, sessile to short-pedunculate (peduncles 0.2–
4 cm long) racemes or spikes (rarely panicles); ovary symmetric,
stigma 2-lobed (one lobe usually bifid) or subcrateriform (in
S. guianensis), lobes not subcapitate; widespread .......Staurogyne
7 Stamens 4, sometimes also with an additional staminode ........... 8
7 Stamens 2, sometimes also with (1) 2 (3) staminodes............... 30
8 Anthers all monothecous; plants without cystoliths .................... 9
8 Anthers all bithecous or 2 bithecous and 2 monothecous; plants
with cystoliths ............................................................................ 14
9 Corolla zygomorphic, the lobes dissimilar in form ................... 10
9 Corolla usually subactinomorphic, the lobes more or less similar in
form ........................................................................................... 12
10 Calyx deeply 3-partite; Colombia...........................Cyphacanthus
10 Calyx 5-partite ........................................................................... 11
11 Leaves opposite (rarely subopposite); bracts entire or dentate, green
or often brightly colored; corolla rarely with linear nectar guides,
mostly 25–85 mm long ;at least distal portion of filaments of stamens
usually exserted from corolla tube; pollen with colpi not expanded or
bifurcating (usually narrowed) toward poles, interapertural exine usu-
ally h eterogeneously scul ptured; widespread ........... Aphelandra [5]
11 Leaves opposite (rarely subopposite) or quaternate; bracts entire
and usually green; corolla often with colored linear nectar guides,
6.5–24 mm long (or if larger, to 40 mm, then plants with quater-
nate leaves); filaments of stamens often entirely included in corolla
tube; pollen with colpi sometimes expanded or bifurcating toward
poles, interapertural exine homogeneously sculptured; Mexico.....
................................................................................... Holographis
12 Pollen 3-colpate with each colpus longitudinally bisected by an oper-
culum (elongate band of exine), opercula either isolated within the
colpi (operculate) or connected at each end to the interapertural exine
(pontoperculate); Jamaica ............................................... Salpixantha
12 Pollen 3-colpate with colpi not bisected by elongate bands of exine
or pollen pantoforate (i.e., sometimes in Stenandrium dulce)or
pollen pantoaperturate (rugate) with rugae arranged ± tangentially
over surface or pollen 3-colpate and with prominent margines and
mesocolpial ridges (appearing 9-colpate); widespread, but not in
Jamaica ...................................................................................... 13
13 Plants usually small, up to 25(–70) cm; leaves often borne at or
near ground level (plants acaulescent to subcaulescent); bracts
usually green; pollen 3-colpate or pantoforate (i.e., sometimes in
S. dulce)....................................................................Stenandrium
13 Plants usually shrubby, up to 1.5 m tall; leaves disposed along con-
spicuous stems; bracts whitish, pinkish, or reddish-brown; pollen
pantoaperturate (rugate) with rugae arranged ± tangentially or pol-
len 3-colpate and with prominent margines and mesocolpial ridges
(appearing 9-colpate)........................................ Neriacanthus [6]
14 Stamens with 2 anthers bithecous and 2 anthers monothecous...15
14 Stamens with all anthers bithecous............................................ 20
15 Seeds with hygroscopic trichomes; corolla with quincuncial aesti-
vation............................................................................................... 16
15 Seeds without hygroscopic trichomes; corolla with ascending-
cochlear aestivation ................................................................... 17
16 Calyx lobes ± homomorphic; plants with axillary spines and/or
spiny leaf margins; West Indies.....................................Barleriola
16 Calyx lobes heteromorphic in 2 + 2 + 1 configuration, posterior
lobe broadest, lateral lobes narrowest, anterior lobes often partia-
lly fused; plants lacking axillary spines and/or spiny leaf margins;
widespread........................................................ Lepidagathis [58]
17 Corolla red, colored markings on limb absent, 34–48 mm long,
± tubular or clarinet shaped with the tube elongate, relatively slen-
der but gradually expanded distally and the limb shallow, incon-
spicuous, tube 6–11× longer than limb; Bolivia, Brazil ................
.............................................................................Pranceacanthus
17 Corolla white, pinkish or purple, often with colored markings on
limb, 10–45 mm long, infundibuliform to salverform and with a
± conspicuous limb (at least the upper lip in Isotheca), tube 1–
2.6 (–3.6) × longer than limb (or if 6 or more times longer than
limb as in Isotheca, then corolla white)..................................... 18
18 Corolla white, apparently lacking colored markings on limb, 35–
45 mm long, downward curved and “cobralike”in bud; stamens
conspicuously exserted beyond limb of corolla; inflorescence a
± open, terminal dichasiate raceme (i.e., dichasia sessile and flowers
pedicellate); pollen 4-aperturate, echinate; Trinidad, Venezuela......
.............................................................................................Isotheca
18 Corolla white, pinkish or purple, usually with colored markings on
limb, 10–30 mm long, usually straight, not “cobralike”in bud; sta-
mens included in corolla tube or exserted from it, but not extending
beyond limb; inflorescence of axillary or usually terminal dichasi-
ate spikes (sometimes very reduced) or panicles of spikes; pollen
usually 3-aperturate ................................................................... 19
19 Corolla ± salverform with subactinomorphic limb, upper lip deeply
lobed; bracts ± inconspicuous, ca. 1 mm wide; Costa Rica, Brazil,
Panama ........................................................... Chamaeranthemum
19 Corolla infundibuliform with bilabiate limb, upper lip entire to
shallowly lobed; bracts conspicuous, (2–)5–20 mm wide; wide-
spread .....................................................................Herpetacanthus
20 Corolla with ascending-cochlear aestivation; pollen 3-colporate,
6-pseudocolpate......................................................................... 21
20 Corolla with quincuncial or left-contort aestivation; pollen
otherwise ................................................................................... 22
21 Perennial herbs or shrubs to 1.5 m tall; calyx to 5 mm long, 5-lobed,
lobes homomorphic; corolla red, 15–21 mm long; capsule 12–
18 mm long; seeds permanently retained in capsule and partially
fused to inner capsule wall; western Mexico ..........Chalarothyrsus
21 Large shrubs to small trees to 8 m tall; calyx 15–40 mm long,
2-lipped, the 2 segments entire or variously lobed at apex; corolla
white to yellow; 23–97 mm long; capsule 40–85 mm long; seeds
expelled from mature capsule, not fused to inner capsule wall; east-
ern and southern Mexico to Costa Rica................. Spathacanthus
22 Corolla with quincuncial aestivation, lacking a filament curtain;
inflorescences mostly secundiflorus ......................... Lepidagathis
22 Corolla with left-contort aestivation, with a filament curtain; inflo-
rescences rarely (if ever) secundiflorus ..................................... 23
23 Calyx 3-lobed; corolla very large, gullet-shaped, pale green to greenish-
yellow (sometimes with maroon tinges), cream-colored, or entirely
dark maroon; Mexico and Central America ..................... Louteridium
23 Calyx 5-lobed; corolla variable but not as above....................... 24
24 Corolla subcylindrical or, if with an expanded/ampliate throat, then
flowers borne in headlike clusters subtended by several pairs of
bracts ......................................................................................... 25
32 Version of Record
Manzitto-Tripp & al. •Revised classification and keys to Acanthaceae TAXON 00 (00) •1–51

24 Corolla campanulate, throat ampliate; flowers not borne in head-
like clusters, not subtended by several pairs of bracts............... 26
25 Thecae awned basally; western South America..... Suessenguthia
25 Thecae awnless; Peru.......................................... Trichosanchezia
26 Calyx lobes fused for at least 1/3 of their length and usually over half
of their length, with hyaline regions bordering each lobe; anther the-
cae usually appendaged at base, these sometimes inconspicuous or
rarely absent; plants herbaceous or subshrubby............ Dyschoriste
26 Calyx lobes deeply divided, or if with a conspicuous fused portion
then lacking hyaline regions bordering each lobe; anther thecae
lacking basal appendages or if basally awned (Bravaisia) then
plants large shrubs or trees ........................................................ 27
27 Thecae awned with a single, subulate projection ...........Bravaisia
27 Thecae awnless.......................................................................... 28
28 Shrubs or trees up to 25 m tall and usually ≥4 m tall; corolla
woolly pubescent externally .....................................Trichanthera
28 Herbs, shrubs, sometimes clambering, or treelets, <4 m tall; coro-
lla various but not woolly pubescent externally......................... 29
29 Corolla usually ≤10 mm long, conspicuously bilabiate; plants usu-
ally aquatic or semi-aquatic; pollen 4-colporate and 8- (or more?
[59]) pseudocolpate, exine usually more or less finely and irregu-
larly reticulate ..............................................................Hygrophila
29 Corolla usually >10 mm long, subactinomorphic and not conspic-
uously bilabiate; plants not aquatic but can be riparian; pollen
3-aperturate, lacking pseudocolpi, exine coarsely reticulate .........
........................................................................................... Ruellia
30 Corolla with left-contort or quincuncial aestivation, with or with-
out a f ilament curtain................................................................. 31
30 Corolla with ascending-cochlear aestivation, lacking a f ilament
curtain........................................................................................ 34
31 Corolla with quincuncial aestivation, lacking a filament curtain..... 32
31 Corolla with left-contort aestivation, with a filament curtain.... 33
32 Corolla red, strongly bilabiate, upper lip ± hooded, entire or shal-
lowly 2-lobed, lower lip 3-lobed; Mexico ................ Lepidagathis
32 Corolla bright yellow (drying dark purplish), consisting of 5, large,
spreading lobes, 4 posterior, 1 anterior; widespread ........Barleria
33 Calyx 3-partite; corolla very large, gullet-shaped, pale green to
greenish-yellow (sometimes with maroon tinges), cream-colored,
or entirely dark maroon; primarily nocturnal; shrubs to trees; pol-
len spherical and pantoforate; Mexico and Central America.........
...................................................................................Louteridium
33 Calyx 5-partite; corolla long and tubular, primarily red or orange,
but can be yellow or white; shrubs; pollen not spherical, 2-colporate
and polypseudocolpate, the apertural faces oriented 90° from one
another; mostly South America........................................Sanchezia
34 Androecium of 2 stamens (bithecous) and 2 staminodes; flowers
sometimes heterostylous ............................................................ 35
34 Androecium of 2 stamens (bithecous or monothecous) and 0 sta-
minodes; flowers not heterostylous ........................................... 41
35 Corolla ca. 5 mm long; upper lip divided less than 1/3 its length
(i.e., shallowly 2-lobed); Ecuador........................ Psilanthele [60]
35 Corolla (at least of chasmogamous flowers) >5 mm long (up to
45 mm long and usually >10 mm long); upper lip divided 1/2 or
more its length (shallowly 2-lobed in Chileranthemum and some
species of Odontonema) ............................................................ 36
36 Corolla with purplish spots on limb, the 2 lobes of upper lip stron-
gly laterally divergent from each other; stamens conspicuously ex-
posed between lipsof corolla (not appressed to upper lip of corolla),
filaments arched toward lower lip of corolla; plants not heterosty-
lous; South America..................................................Pulchranthus
36 Corolla with or without spots on limb, the 2 lobes of upper lip not
laterally divergent from each other; stamens appressed to upper lip
of corolla or exposed between lips, filaments straight (not curved to-
ward lower lip of corolla); plants often heterostylous...................37
37 Corolla ± salverform, tube elongate and cylindric (or throat be-
coming slightly expanded) or sometimes narrowed distally, limb
± rotate, usually subactinomorphic..................Pseuderanthemum
37 Corolla infundibuliform, tube expanding gradually or ± abruptly
toward mouth (sometimes subcylindric), limb extending forward
to reflexed, bilabiate .................................................................. 38
38 Trailing or clambering shrubs; leaves coriaceous, blades 10–25 mm
long; corolla 13–17 mm long; serpentine substrates in Cuba ...........
.............................................................................................. Sapphoa
38 Plants lacking the above combination of characters .................. 39
39 Armature usually present in leaf axils (absent in some plants or in
some species); leaves usually coriaceous; corolla usually bluish to
purple (rarely red or white); Argentina, Bolivia, Peru, West Indies
.................................................................................. Oplonia [61]
39 Spines absent; leaves membranaceous; corolla red, purplish, pink,
yellow, or white ......................................................................... 40
40 Corolla purplish to pinkish to whitish with colored markings on
the lower lip, tube subcylindric to ± abruptly expanded distally, shor-
ter to only slightly longer than limb, upper lip shallowly 2-lobed,
erect, lower lip horizontally spreading (i.e., lips 90° apart with lower
lip forming a conspicuous “landing platform”); plants not clamber-
ing; Mexico to El Salvador.....................................Chileranthemum
40 Corolla red, pinkish, or purplish (rarely yellow or white), usually
lacking colored markings, tube usually gradually expanded dista-
lly and longer (often >1.5× longer) than limb, upper lip shallowly
to ± deeply 2-lobed, upper and lower lips variously oriented; plants
sometimes clambering; widespread .......................... Odontonema
41 Anthers monothecous ................................................................ 42
41 Anthers bithecous ...................................................................... 43
42 Inflorescence of terminal spikes; corolla violet, tube cylindric,
limb deeply 5-lobed with equal lobes; Brazil ................................
............................................................Sebastiano-Schaueria [62]
42 Plants not with the above combination of characters; wide-
spread.......................................................................Stenostephanus
43 Stems usually hexagonal; flowers in bracteate dichasia bearing 1
or more cymules, cymules of 1 or more flowers subtended by an
involucre of 2 or more pairs of bracteoles (outer pair usually con-
spicuous and larger than inner pair(s)); capsules with fracturing
placentae, dehiscent capsule conspicuously ruptured near base of
head; corolla resupinate (180° or 360°) in some species; wide-
spread ............................................................................ Dicliptera
43 Stems terete to quadrate to quadrate-sulcate (rarely subhexagonal);
flowers rarely borne in cymules but, if so, then not as described
above; capsules without fracturing placentae (or retinacula slightly
separating from inner wall in Henrya and Tetramerium, but then
not rising to protrude prominently from each capsule valve on/after
dehiscence); corolla not resupinate............................................ 44
44 Corolla subsalverform, purplish; stamens 2–2.5 mm long, filaments
apically pubescent with flexuose eglandular trichomes, thecae su-
perposed (0.3–0.5 mm apart), distal theca fertile, proximal theca
sterile (appendage-like); seeds ca. 5 mm in diam., papillose, mar-
gin swollen............................................................. Streblacanthus
44 Plants not with the above combination of characters................. 45
45 Upper lip of corolla with a rugula on the internal surface (not con-
firmed for all taxa); flowers nototribic; anther thecae with or without
basal appendages, the pair parallel to perpendicular and equally to
unequally inserted on the filament; pollen 2–6 (or more?)-apertu-
rate, pseudocolpi present or absent, insulae (i.e., ± isolated [some-
times linked in Poikilacanthus] [63] gemmate regions enclosed by
thick, smooth marginal walls) and/or peninsulae (attached on one
side to the interapertural exine), when present, usually restricted to
1 or more rows flanking apertures or entire interapertural surface
either reticulate or covered with smooth and subconic to rounded
verrucae..........................................................................................46
45 Upper lip of corolla lacking a rugula; flowers sternotribic, nototribic
or pleurotribic; anther thecae lacking basal appendages, the pair par-
allel to subsagittate and equally to subequally inserted on the fila-
ment; pollen 3-colporate and 6-pseudocolpate (pseudocolpi
sometimes fused, inconspicuous, or rarely absent; 2-colporate, 4-
pseudocolpate in Mexacanthus), insulae and peninsulae absent ... 53
Version of Record 33
TAXON 00 (00) •1–51 Manzitto-Tripp & al. •Revised classification and keys to Acanthaceae

46 Shrubs or epiphytic herbs; flowers subtended by an involucre of
conspicuous, basally fused bracteoles; corolla red or lilac; calyx
highly reduced, cupular, entire to shallowly dentate; Brazil..........
.................................................................................... Clistax [64]
46 Plants not with the above combination of characters................. 47
47 Inflorescence of short, axillary, pedunculate, subcapitate spikes;
bracts oblanceolate to obovate; thecae of a pair superposed and
perpendicular; corolla yellow-green with purplish spots on lower
lip, ca. 9 mm long; Andean Peru .........................Cephalacanthus
47 Plants not with the above combination of characters................. 48
48 Trees to 5 m tall; leaves with globose (appearing hemispheric on
surfaces) concretions 0.3–0.7 mm in diam.; thecae of a pair equally
inserted, parallel to subsagittate, lacking basal appendages; calyx
25–32 mm long, lobes oblong to oblanceolate, widely spreading
at maturity; capsule 22–29 mm long; Haiti ..............Samuelssonia
48 Plants not with the above combination of characters................. 49
49 Pollen 4–6 (or more?)-porate, interapertural surfaces either cov-
ered with discrete insulae or with insulae linked by sharing com-
mon end-walls and arranged in loops that enclose a row or band
of linked insulae ........................................................................ 50
49 Pollen 2–4-aperturate (colporate or porate), apertures flanked by
pseudocolpi or by 1 or more rows of ± discrete insulae and/or pe-
ninsulae, or the entire interapertural surface covered with smooth
and subconic to rounded verrucae ............................................. 51
50 Inflorescence large, usually longer than 7 cm, and very showy with
conspicuous subfoliose red to maroon to pinkish bracts and brac-
teoles; corolla white (sometimes turning pinkish with age); pollen
covered with discrete insulae; frequently cultivated, presumably
native in Venezuela ...................................... Megaskepasma [65]
50 Inflorescence various, but not as described above, usually less than
7 cm long; corolla red, orangish, pink, pinkish-purple, greenish-
yellow, or white; pollen covered with discrete insulae or pollen
otherwise; widespread ........................................... Poikilacanthus
51 Erect shrubs to 3 m; corolla primarily nocturnal, greenish, pale
yellow, or cream, 38–95 mm long, upper lip arched, lobes of lower
lip usually dangling and somewhat twisted; thecae 5–7.6 mm long;
pollen 3-colporate and with either a pseudocolpus or 1 row of insu-
lae flanking each colporus; Brazil ..................... Harpochilus [66]
51 Plants not with the above combination of characters................. 52
52 Subscandent shrubs; corolla greenish white, 13–14 mm long, up-
per lip erect (i.e., continuous with tube) and lower lip horizontal
at maturity (i.e., spreading 90° from upper lip); pollen 4-colporate,
mesocolpia “occasionally”[fide Raj, 1961] with 2 pseudocolpi;
Cuba................................................................................... Dasytropis
52 Plants not with this combination of characters and extremely vari-
able in vegetative, floral, and palynological morphologies; wide-
spread ........................................................................ Justicia [67]
53 Inflorescence a terminal thyrse; corolla bud strongly arched (i.e.,
curved downward and appearing like an upside-down hook), open
corolla with the limb curved downward forming an upside-down
“U”or semi-circle; thecae 5–6 mm long; Cuba ..... Ancistranthus
53 Plants not with the above combination of characters; not occurring
in Cuba ...................................................................................... 54
54 Bracteoles of a pair fused along one side from base to near apex form-
ing a sheathing involucre around flower; pollen with colpi broad, far
exceeding the width of the centrally positioned ora; septa and attached
retinacula separating slightly from inner wall of mature capsules near
base of head; U.S.A. (Arizona) to Costa Rica........................ Henrya
54 Bracteoles of a pair not fused, or if so only at base up to 1 mm; pol-
len with colpi narrow, not or only slightly exceeding width of cen-
trally positioned ora; septa and attached retinacula not separating
from inner wall of mature capsules (except in Tetramerium).......55
55 Capsules progressively reflexing during maturation (upside-down
at maturity), distal portion of capsule expanded, truncate and widest
at apex, basal portion of capsule densely pubescent with apically
hooked (uncinate) trichomes; seeds 2, permanently enclosed in cap-
sule valves; northwestern Mexico ........................... Aphanosperma
55 Capsules not reflexed at maturity, distal portion of capsule tapering
to a point or rounded at apex, basal portion lacking uncinate tricho-
mes; seeds 2–4, free from capsule valves when mature ............ 56
56 Flowers sternotribic (i.e., stamens positioned near lower lip of co-
rolla and anthers dehiscing toward upper lip) or pleurotribic (i.e.,
anthers dehiscing toward center of floral axis and each other); pri-
marily North and Central America ............................................ 57
56 Flowers nototribic (i.e., stamens positioned near upper lip of corolla
and anthers dehiscing toward lower lip) or sternotribic in Schaueria
litoralis from South America; mostly South America ..................61
57 Flowers pleurotribic; seeds usually 2 per capsule...................... 58
57 Flowers sternotribic; seeds 2–4 per capsule............................... 59
58 Corolla 6.5–11 mm long, cream with maroon markings; pollen 3-
colporate, 6-pseudocolpate; southern Mexico ........ Gypsacanthus
58 Corolla 17–26 mm long, bicolored with upper lip red and lower lip
yellow; pollen 2-colporate, 4-pseudocolpate; west-central Mexico
................................................................................. Mexacanthus
59 Inflorescence of usually densely bracteate, 4-sided spikes; bracts
conspicuous, usually concealing the calyx; septa and attached reti-
nacula separating slightly from inner wall of mature capsules near
base of head .............................................................. Tetramerium
59 Inflorescence neither densely bracteate nor 4-sided; bracts incon-
spicuous and sometimes caducous, not concealing the calyx; septa
and attached retinacula not separating from inner wall of mature
capsules ..................................................................................... 60
60 Shrubs to 4 m tall, rarely dying back to woody caudices; corolla
(white) pink, red, or orange (yellowish), lacking conspicuous col-
ored markings, (24–)30–65 mm long, tube usually conspicuously
ampliate toward apex, (10–)14–31 mm long; thecae 2.2–4.8 mm
long; U.S.A. to Costa Rica ......................................Anisacanthus
60 Perennial herbs to weak shrubs up to 1 (–1.5) m tall, usually dying
back to woody caudices; corollawhite, yellow, blue, purple, or pink-
ish, usually with conspicuous colored markings on the limb, 5.5–23
(–27) mm long, tube not or only slightly ampliate toward apex, 1.5–
8.5 (–13) mm long; thecae 0.5–1.9 mm long; widespread...............
.....................................................................................Carlowrightia
61 Creeping perennial herbs; leaves with conspicuous white, pink, or
red veins; corolla yellow, 10–15 mm long; inflorescence of den-
sely bracteate terminal spikes; Colombia and Brazil to Bolivia ....
.......................................................................................... Fittonia
61 Plants not with the above combination of characters................. 62
62 Inflorescence of axillary and terminal, densely bracteate spike-like
thyrses to 15 cm long; bracts and calyx lobes distally dark maroon;
corolla yellow, (28–)35–47 mm long, throat abruptly and broadly
expanded from subcylindric tube, appearing saccate; northeastern
Mexico........................................................................ Hoverdenia
62 Plants not with the above combination of characters [68] ......... 63
63 Shrubs; bracts and bracteoles inconspicuous and often caducous,
0.8–3 mm long, 0.2–1 mm wide; corolla red, 20–45 mm long; sea-
sonally dry forests of Argentina, Bolivia, Brazil, Paraguay ..........
..................................... Thyrsacanthus (in part, excl. T. sulcatus)
63 Plants not with the above combination of characters................. 64
64 Corolla subsalverform, tube elongate, 1.3–8.5× longer than limb,
narrow (up to 1.5 mm in diam. near midpoint, measured flat),
and cylindric for most of its length (± abruptly expanded only near
apex, if at all) ............................................................................. 65
64 Corolla infundibuliform, tube ± gradually expanded distally, 0.7–3
(–3.6) × longer than limb, mostly neither conspicuously narrow
([1.2–] 1.5–6.3 mm in diam. near midpoint, measured flat) nor
cylindric through most of its length .......................................... 67
65 Inflorescence of open and elongate spikes, bracts inconspicuous,
rachis clearly visible; corolla tube 3–8.5× longer than limb;
Costa Rica to Argentina......................Pachystachys (in part [69])
65 Inflorescence of densely and conspicuously bracteate ± 4-sided spi-
kes, rachis not visible; corolla tube 1.3–3× longer than limb..... 66
66 Bracts lanceolate, 2–4 mm wide; Argentina, Paraguay, Uruguay ....
................................................................... Thyrsacanthus sulcatus
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66 Bracts ovate, broadly ovate, subdeltate, elliptic or subcircular, 5–
18 mm wide; U.S.A. to Mexico ....................................... Yeatesia
67 Corolla bluish or purplish, 11–21 mm long; arid regions of north-
ern Mexico ................. Mirandea (in part, excluding M. sylvatica)
67 Corolla white, yellow, orangish, red or pink, 8–70 mm long; plants
of moist to wet forests in southern Mexico to South America .....68
68 Corolla yellow to white, 8–31 mm long; Mexico, Guatemala .....69
58 Corolla white, yellow, orangish, red or pink, 10–70 mm long; South
America and the West Indies ...................................................... 70
69 Bracts 1–4 mm long, 0.5–0.8 mm wide; calyx 2–3.7 mm long; coro-
lla 8–13.5 mm long; southern Mexico..........Mirandea sylvatica [70]
69 Bracts 9–22 mm long, 1.2–2.2 mm wide; calyx 10–25 mm long;
corolla 22–31 mm long; Mexico, Guatemala ................................
..............................................................Schaueria parviflora [71]
70 Corolla yellow or white; bracts narrow, 0.5–2.5 mm wide, mostly
yellow in species with yellow corollas and green in species with
white corollas; Atlantic forests of Brazil ...................... Schaueria
70 Corolla mostly red, orange-red or pink (white in P. lutea, and yel-
low in P. azaleiflora); bracts (4–)6–18 mm wide in most species
(1–1.5 mm wide in P. azaleiflora,P. badiospica,P.gracilis and
P.linearibracteata), green to yellowish-green (bright yellow to
orange-yellow in P. lutea and brownish red in P. badiospica); West
Indies and Amazonian South America, especially Peru ................
................................................................................. Pachystachys
Notes corresponding to keys
[1] Physacantheae is here recognized for the first time (see Validation
of Names) to accommodate three species of Physacanthus, a line-
age of proposed wide-hybrid origin (Tripp & al., 2013b) between
unknown progenitors of Acantheae and Ruellieae.
[2] See also the keys in Daniel & McDade (2014) and Braz & al.
(2021), which provide additional information useful for identify-
ing genera in this lineage, especially with respect to bract, seed,
and pollen morphology.
[3] This condition occurs for example in Crossandra flava Hook. and
Sclerochiton uluguruensis Vollesen from continental Africa.
[4] Molecular evidence (McDade & al., 2005) indicates that the Afro-
Malagasy species of Stenandrium, including the Malagasy segre-
gate genus Achyrocalyx, for m a clade distinct from NW Stenandrium
and should be treated under the genus Stenandriopsis.However,no
morphological characters have so far been identified to support the
separation of Stenandriopsis from caulescent species of Stenan-
drium, which was the basis for Vollesen’s (1992) uniting of the two.
[5] Plants previously treated in Encephalosphaera,Geissomeria,Rhom-
bochlamys,Orophochilus, and Xantheranthemum cannot reliably
be differentiated from those of Aphelandra using either micro- or
macromorphological means; moreover, phylogenetic (McDade &
al., 2005) evidence suggests some of these taxa are likely to be best
considered under Aphelandra (some have already been combined
in prior works), hence these genera are here treated within Aphelan-
dra s.l. (see also Wasshausen, 1996).
[6] The type of Neriacanthus,N. purdieanus Benth. & Hook.f., is conge-
neric with Salpixantha. The Central and South American species
of “Neriacanthus”as keyed out here may need to be accom-
modated under a new generic name unless Neriacanthus is con-
served with a different type (see Franck & Daniel, 2015). More
molecular work for the continental taxa is needed prior to taxonomic
re-assignments.
[7] The five genera allied to Crabbea that are considered to be ende-
mic to Madagascar are poorly delimited morphologically and
may ultimately be united under a single genus; they are, however,
here upheld pending further molecular phylogenetic evidence (see
Onjalalaina & Darbyshire, 2016).
[8] Preliminary observations including chemical treatments on leaves
of the genus Podorungia from Madagascar indicate a potential ab-
sence of cystoliths in two species (I. Darbyshire, unpub. data), but
further study is needed.
[9] Haplanthus has recently been resurrected from Andrographis based
on morphological characters (Gnanasekaran & al., 2016) but this
merits evaluation via phylogenetic analyses of molecular data.
[10] Only the type of Sphinctacanthus,S. griffithii, is here included
in our concept of this genus (see Hansen, 1985b; McDade & al.,
2018).
[11] Andrographis here includes Indoneesiella, which was previously
separated on the basis of having 2 ovules per locule (capsule 4-
seeded), versus 3 or more ovules per locule (capsule 6–20-seeded)
in Andrographis s.str. The two are separated in the key to Asian
genera as Indoneesiella is upheld by some authors.
[12] Phlogacanthus here includes Cystacanthus; they were previously
separated (e.g., in Hu & al., 2011) by differences in the shape of
the corolla tube: cylindrical and gradually widened towards the
mouth and straight in Phlogacanthus, abruptly saccate and geni-
culate above the middle in Cystacanthus. However, emerging
molecular evidence indicates that these two genera are congeneric
(see Deng & al., 2020).
[13] Genera of Whitfieldiinae are not well circumscribed, particularly
in Madagascar where the endemic genera Camarotea,Forcipella,
Leandriella,Vindasia, and Zygoruellia are very close morpholog-
ically. These entities may ultimately be best treated under a single
genus, and Zygoruellia has nomenclatural priority.
[14] An unmatched Malagasy species with corollas similar to Lean-
driella (but lacking long white trichomes on the internal surface
of the corolla lobes) has not yet been reliably placed to genus.
[15] We have been unable to uncover any morphological characters to
separate Forcipella and Vindasia (see note 13).
[16] “Pseudosiphonium ined.”was a tentative descriptor proposed in
Tripp & al. (2013a) to accommodate plants from China previously
ascribed to Ruellia venusta Hance or Leptosiphonium venustum
(Hance) E.Hossain that differ from the latter in several features.
It has not yet been formally described and is here mentioned only
within the Key to Genera of Ruellieae. That is, the inclusion of
this name in the present study does not indicate acceptance of
the name by the authors of this paper.
[17] Genera within Strobilanthinae have remained poorly delimited,
and phylogenetic evidence (Moylan & al., 2004) suggests Strobi-
lanthes is best delimited to include previously segregated genera
(i.e., Clarkeasia,Hemigraphis, and Stenosiphonium, which appear
to differ from Strobilanthes s.str. primarily in having >4 ovules per
ovary). As such, we here recognize a broadened concept of Strobi-
lanthes—one that includes these three genera. However, we refrain
from making a long series of necessary combinations, for which
additional, focused, phylogenetic and nomenclatural work outside
the scope of the present study will be required.
[18] The lip of Eremomastax can sometimes be held in the upper posi-
tion (i.e., is resupinate) due to twisting of the corolla tube.
[19] Calacanthus is resolved as sister to Acanthopale in the RADseq
results of Tripp & Darbyshire (2020) with strong support and so
is tentatively placed within Ruelliinae in the current classifica-
tion. However, morphological characters point towards a closer
affinity to Hygrophilinae (Tripp & al., 2013a). The placement of
Calacanthus within Ruelliinae should therefore be considered
provisional.
[20] Endosiphon primuloides T.Anderson ex Benth. was transferred to
Ruellia by Heine (1966) as they share the same pollen type (spher-
oid, coarsely reticulate) but the zygomorphic calyx of Endosiphon
is very close to Dischistocalyx, and E. primuloides is a forest spe-
cies like members of Dischistocalyx and unlike most African
species ofRuellia. This species needs to be included in a future phylo-
genetic analysis to confirm its placement. Endosiphon may ultimately
need to be resurrected.
[21] “Sinoacanthus ined.”was a tentative descriptor proposed in Tripp
& al. (2013a) to accommodate plants from China previously as-
cribed to Echinacanthus that differ from the latter in several fea-
tures including pollen morphology. “Sinoacanthus ined.”has not
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yet been formally described and as such is here mentioned only
within the Key to genera of Ruellieae. That is, the inclusion of this
name in the present study does not indicate acceptance of the name
by the authors of this paper.
[22] In limited instances, species of Dyschoriste lack anther append-
ages, such as D. mutica.
[23] We here include Ionacanthus within Mimulopsis for the first time,
and provide the new combination. In Tripp & al. (2013a), Iona-
canthus was synonymized within Mellera, but subsequent RADseq
data (Tripp & Darbyshire, 2020) demonstrated that Ionacan-
thus is instead nested within Mimulopsis, with which it more
closely aligns morphologically, particularly with regard to stamen
morphology.
[24] Mellera congdonii Vollesen is excluded from the circumscription
of Mellera here as it has traits more closely allied to Mcdadea;
see Tripp & Darbyshire (2020).
[25] Filaments of flowers of Xylacanthus were not described in the pro-
tologue. However, its morphological affinity to Strobilanthes as
well as to Echinacanthus suggests high likelihood of phylogenetic
placement of this lineage within core Ruellieae (i.e., among the
subtribes phylogenetically derived with respect to Erantheminae,
whose members lack filament curtains except for Eranthemum
and Kosmosiphon). Additionally, although pollen morphology of
Xylacanthus was not depicted in the protologue, the authors de-
scribe it as similar to that of Echinacanthus (Averyanov & al., 2018).
[26] This entry refers to Filetia africana Lindau, currently treated under
Asystasia lindauiana Hutch. & Dalziel, but the anthers with offset
thecae and the slender racemose thyrse are quite different to other
species in Asystasia, and show similarities with Asian Filetia (for
which, see the note in the key to Asian genera).
[27] Asystasia is here treated in the broad sense and includes a number
of previously separated small genera, including Salpinctium and
Asystasiella.Asystasia encompasses considerable variation in in-
florescence form, corolla morphology, and pollen type. Glossochi-
lus may also be included within Asystasia in the future, but we
maintain it in this work, pending further molecular analyses.
[28] Ruellia heterosepala Benoist from Madagascar would key out
here, but is otherwise very different to Dinteracanthus, for exam-
ple, in being largely glabrous, having anisophyllous leaves, and
bearing smaller corollas. It is likely to represent an as yet unde-
scribed genus.
[29] Two species of Mimulopsis from the Uluguru Mts. of Tanzania,
M. macrantha (Mildbr.) E.Tripp and M. marronina (Vollesen)
E.Tripp (previously treated in the segregate genus Epiclastop-
elma), lack spurred outer thecae on the two longer stamens, which
are otherwise characteristic of Mimulopsis. These two species are
morphologically close to Heteradelphia and the relationship be-
tween these taxa requires further investigation. Note that the type
of Epiclastopelma,E. glandulosum Lindau (= Mimulopsis volle-
seniana E.Tripp & T.F.Daniel), does have spurred anthers and is
morphologically similar to some Malagasy species of Mimulopsis.
[30] It is not certain that the Malagasy species Ruspolia humbertii Ben-
oist is best treated within this genus; it differs from other species of
Ruspolia in having clearly exserted stamens, a markedly bilabiate
corolla with the upper two lobes partially fused, and a curved co-
rolla tube.
[31] Monothecium leucopterum Benoist from Madagascar would key here
but this species is morphologically very different from the two conti-
nental African species, and probably belongs within Anisostachya.
[32] Ritonia is a poorly known genus and its tribal placement is un-
clear. The combination of glomerules of flowers each with small
subtending clasping pairs of bracteoles and spheroid, 2-porate pol-
len suggest affinity with Whitfieldiinae but the corollas are unlike
anything in that subtribe. The fruits are unknown, and corolla aes-
tivation of Ritonia is not clear from specimens. Therefore, poten-
tial affinity with Isoglossinae cannot be entirely dismissed. This
description refers only to R. humbertii Benoist (the type of the
genus) and R. barbigera Benoist. The other two species described
by Benoist are quite different. Ritonia rosea Benoist is considered
to be a synonym of Populina perrieri (Madagascar Catalogue,
2020), while R. poissionii Benoist is considered to belong in core
Isoglossinae (I. Darbyshire, pers. obs.).
[33] To our knowledge, only one species of Lepidagathis in Africa and
Madagascar has 2 stamens + 2 staminodes: L. grandidieri Benoist
from Madagascar.
[34] Stearn (1971) included Forsythiopsis from Madagascar within
Oplonia from the NW. While the two have similar floral morpho-
logies, molecular evidence indicates that they do not form a mono-
phyletic clade (McDade & al., 2021). Morphologically, Malagasy
Oplonia is similar to Pseuderanthemum, particularly to the short-
tubed P. campylosiphon Mildbr. from Tanzania, differing prima-
rily in inflorescence form.
[35] Vavara is very close to Dicliptera and may prove to be a member
of that genus, but the anther character is a notable morphological
difference.
[36] Peristrophe is not recognized as separate from Dicliptera in this
classification but is included in the key here as it is maintained
by some scholars. Most Asian members of Peristrophe have linear
anther thecae, quite different from the elliptic to rounded thecae of
Dicliptera and African Peristrophe. This Asian group of Peris-
trophe may be a distinct taxon.
[37] Molecular evidence places Anisotes perplexus T.F.Daniel, Letsara
& Martín-Bravo and a second, undescribed species with a match-
ing corolla form from Madagascar in Isoglossinae and this is sup-
ported by pollen morphology (Kiel & al., 2017; McDade & al.,
2021). The similar corolla form to Anisotes in Justiciinae is almost
certainly an adaptation to bird pollination in both lineages.
[38] Species currently placed in Anisotes and Metarungia share the same
corolla form, which is likely an adaptation to bird pollination. Metar-
ungia is not upheld as distinct from Anisotes by some authors, but
Kiel & al. (2017) find that members of Metarungia form a clade with
Rungia, with which they share capsules with fracturing placentae.
[39] The genera within core Isoglossinae from Africa and Madagascar
with bithecous stamens are not well differentiated and may be best
treated as a single genus (Isoglossa), but preliminary molecular re-
sults indicate that Isoglossa is paraphyletic. The Malagasy segre-
gate genera Celerina,Melittacanthus, and Sphacanthus are not
keyed out separately here.
[40] Vollesen (1989) noted that in one specimen of Ecbolium flanaga-
nii C.B.Clarke (Comins 1309) some of the flowers have 2 well-
developed staminodes with antherodes in addition to the fertile
stamens; however, this appears to be an aberrant specimen.
[41] We have not been able to reliably distinguish Chorisochora from
Populina on morphological grounds, in part because of the varia-
tion within each of these two genera. Species of Chorisochora
from Socotra and Somalia have anthers held ± perpendicular to
the filament, unlike in Populina where they are parallel or slightly
oblique (although becoming more markedlyoblique with age).The
South African C. transvaalensis (A.Meeuse) Vollesen has ± para-
llel thecae. Daniel & al. (2008) found P. richardii Baill., the type
of the genus, to be included within a well-supported Ecbolium clade
and sister to two Malagasy species of Ecbolium; they therefore con-
cluded that P. richardii should be treated within Ecbolium. McDade
& al. (2018) placed the second species of Populina, P. perrieri, sis-
ter to P. richardii and confirmed placement with the Ecbolium
clade. However, the floral morphology is markedly different to
Ecbolium, although the broadly ovate, palmately veined leaves
are similar to those of some Malagasy species of that genus. The
flowers of P. perrieri look somewhat different to those of P. richar-
dii and are highly reminiscent of Megalochlamys but, unlike in
Megalochlamys, the pollen has pseudocolpi (Muller & al., 1989).
[42] Meiosperma and Pogonospermum were previously united within
Monechma or Justicia sect. Monechma. This group has been the
focus of recent phylogenetic and nomenclatural studies
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(Darbyshire & al., 2020, in press), which revealed that two sepa-
rate clades are involved, and that Monechma s.str. is a later syno-
nym of Meiosperma. Some species of Justicia s.l. with smooth
seeds may key out to one of the two leads in couplet 105, e.g.,
J. crebrinodis Benoist from Madagascar, but these few exceptions
are markedly different morphologically from Meiosperma and
Pogonospermum.
[43] Generic circumscription around OW Justicia is problematic and is
likely to change significantly in the future (see Kiel & al., 2017).
For the present time, we key out only the most commonly segre-
gated genera.
[44] Filetia is only doubtfully distinct from Asystasia. To date, only one
species (F. ridleyi C.B.Clarke) has been included in a phylogenetic
study (McDade & al., 2021) and it was resolved to be nested within
the Asystasia clade.
[45] The tubular calyx is variable in Phialacanthus;itismoststriking
in the type from India, P. griffithii Benth. & Hook.f., where the lobes
are shorter than the tube. Species with a more deeply divided calyx
such as P. minor C.B.Clarke appear very similar to Asystasia.
[46] Plants that key here were formerly treated in the genus Clarkeasia,
which is now considered a synonym of Strobilanthes.
[47] Plants that key here were formerly treated in the genus Stenosipho-
nium, which is now considered a synonym of Strobilanthes.
[48] This refers only to Xerothamnella parvifolia C.T.White; the sec-
ond species in the genus is keyed elsewhere.
[49] Generic delimitation in Graptophyllinae in Asia (and indeed glo-
bally) is not well circumscribed and there are likely to be fewer ge-
nera than currently recognized in couplets 53–58 here.
[50] Most species of Graptophyllum have large, bird-adapted corollas
(see key), but at least three species from Australia, New Guinea,
and Fiji have much smaller, likely insect-pollinated flowers.
[51] Jadunia racemiflora Bremek. from New Guinea would also key out
here; it clearly does not belong within Jadunia s.str., which is a
member of Monotheciinae and lacks staminodes (see key), but the
generic placement of J. racemiflora within Graptophyllinae remains
uncertain.
[52] This refers only to Xerothamnella herbacea R.M.Barker; the sec-
ond species in the genus is keyed elsewhere.
[53] Hansen (1985a) assigned several species with tricolporate-pseudo-
colpate pollen to Isoglossa; he later transferred some of these to
Ptyssiglottis but others currently remain in Isoglossa. We consider
these unlikely to be correctly placed here.
[54] This refers only to Jadunia biroi Lindau; see [61] regarding the
second species treated in Jadunia, which is not considered to be
closely related to J. biroi.
[55] Hu & al. (2011) in Flora of China suggest that Kudoacanthus may
not be distinct from Leptostachya.
[56] Although not included in the NW key, some species of Thunber-
gia, e.g., T. alata Bojer ex Sims and T. fragrans Roxb., are natural-
ized in the Neotropics and, in some locations, extremely weedy;
these would key here with Mendoncia, if included, and can be
readily separated from the latter genus by fruit type.
[57] Whether Nelsonia is native or not in the NW remains unresolved.
[58] We follow Kameyama (2008), who provided the combinations
necessary for recognizing species formerly ascribed to Lophosta-
chys within Lepidagathis.
[59] Hygrophila remains a rather poorly studied genus; as such, the full
range of variation of pollen morphology in this genus remains to
be fully understood.
[60] Generic inconsistencies and species with characteristics inter-
mediate between several genera of American Graptophyllinae (e.g.,
Pseuderanthemum,Odontonema,Chileranthemum,Pulchranthus,
Oplonia) have been noted by several authors (e.g., Baum, 1982;
Daniel, 1995; Daniel & Carrión, 2015; Stearn, 1971). Molecular
phylogenetic studies (McDade & al., 2021) of these and other mor-
phologically similar genera in that subtribe (e.g., Psilanthele,Pul-
chranthus, Sapphoa) reveal that several of the larger genera
(Graptophyllum,Oplonia,Pseuderanthemum) are not monophy-
letic as currently circumscribed. These authors indicated that taxa
and clades of Graptophyllinae are in need of considerable addi-
tional taxonomic and phylogenetic research to resolve monophy-
letic genera in that subtribe.
[61] It remains to be confirmed that two species of Oplonia occurring
in South America (i.e., O. grandiflora (Lindau)Stearn and O. hutchi-
sonii Wassh.) are correctly placed generically, although a third South
American species, O. jujuyensis Wassh. & Ezcurra, is confirmed to
belong in the Oplonia clade (McDade & al., 2021).
[62] American genera of Isoglossinae (e.g., Kalbreyeriella,Sebastiano-
Schaueria,Stenostephanus,Razisea) are not distinct either as cur-
rently circumscribed or based on current taxonomic compositions
of species (see discussions by, e.g., Leonard, 1958; Daniel, 1999;
Wood, 2009; McDade & al., 2018), but Sebastiano-Schaueria is
retained tentatively here, pending further study.
[63] The linked or isolated “insulae”in Poikilacanthus cover the entire
interapertural surface (cf. Daniel, 1991: fig. 1; Daniel, 1998).
[64] Preliminary molecular phylogenetic studies (McDade & al., 2018)
suggest that most (or all) of the NW genera of Justiciinae (e.g.,
Cephalacanthus,Clistax, and excluding Dicliptera; couplets 46–
52) are likely not distinct from Justicia in the broad sense in which
that genus is currently recognized. Additionally, based on molecu-
lar phylogenetic data (Kiel & al., 2018) from two of the three spe-
cies of Clistax, this genus does not appear to be monophyletic.
[65] In his treatment of Nicaraguan Acanthaceae, Durkee (2001) sug-
gested that Perenideboles Ram.Goyena is likely to be a synonym
of Megaskepasma based on descriptive information in the protolo-
gue, but there is no indication in the protologue of the specimens
seen by M. Ramírez Goyena. We follow Durkee’s suggestion here.
[66] Harpochilus is now restricted to two species both of which have bat-
pollinated flowers fide da Costa-Lima & de Oliveira Chagas (2019).
[67] Based on information available, no characters are known to distin-
guish Dichazothece (Brazil) from Justicia and it may belong here,
but further research is required; this genus was recognized by Scot-
land & Vollesen (2000). Monospecific Tessmanniacanthus from
Peru very likely pertains to Justicia (or possibly Tetrameriinae), but
characters that might confirm its placement are not evident either
via characters noted in the protologue or on images of type speci-
mens at G and NY. It is not keyed out separately here, but is ten-
tatively retained in our classification.
[68] South American species described in Thyrsacanthus,Pachysta-
chys, and Schaueria remain in need of additional studies. Côrtes
& al. (2016a) and McDade & al. (2018) note some of the remain-
ing problems among clades containing species placed in these (and
other) genera.
[69] Species previously recognized as Streblacanthus (excluding S. mono-
spermus Kuntze; see Côrtes & al. 2016b).
[70] Molecular phylogenetic data suggest that the southern Mexican
wet-forest species Mirandea sylvatica Acosta is not closely related
to northern Mexican species of this genus, which occur in arid
communities (Kiel & McDade, 2014).
[71] Molecular phylogenetic data suggest that Schaueria parviflora
(Leonard) T.F.Daniel is not closely related to the South American
species of Schaueria (Côrtes & al., 2015; McDade & al., 2018).
IV. Validation of names (tribes, subtribes, genera)
Below, we propose one new tribe (Physacantheae) and three
new subtribes (Lankesteriinae, Whitfieldiinae, Tetrameriinae) of
Acanthaceae along with their validating descriptions. We also
provide emended descriptions for two resurrected and recircum-
scribed subtribes in Justicieae: Graptophyllinae and Monothecii-
nae. Finally, a note on the correct name for the tribe Barlerieae is
provided.
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Physacantheae E.Tripp & I.Darbysh. tr. nov. –Type: Physa-
canthus Benth.
= Haselhoffiinae Lindau in Engler & Prantl, Nat. Pflanzen-
fam., Nachtr. 1: 305. 1897 –Type: Haselhoffia Lindau
(= Physacanthus).
Trailing, decumbent or weakly erect herbs, cystoliths
absent; leaves opposite but sometimes closely spaced and
rosette-forming, often variegated; inflorescences terminal, 1-
to several-flowered; calyces cylindrical or inflated, lobes fused
for most of their length; corolla white to purple, tube narrowly
cylindrical, geniculate at apex, limb subactinomorphic with 5
equal lobes, aestivation left-contort; androecium of 4 stamens
with monothecous anthers plus 1 staminode; stigma clavate,
2-lobed; capsule cylindrical, (4–)6–9-seeded, retinacula pre-
sent, seeds with papillose processes on the surface; pollen with
compound germinal apertures, prolate, 3-colporate with 3
interapertural pseudocolpi.
Barlerieae Nees in Martius, Fl. Bras. 9: 7, 65. 1847 –Type:
Barleria L.
= Russeggereae Meisn., Pl. Vasc. Gen., Tab. Diagn.: 293 &
Comm.: 202. 1840 –Type: Russeggera Endl. (= Lepida-
gathis Willd.).
Perennial, herbs, shrubs or rarely small trees, with cysto-
liths, these sometimes occurring in adjacent cells to form
“double cystoliths”; leaves opposite, sometimes subrosulate;
inflorescences terminal or axillary, varying from flowers soli-
tary to held in complex dichasial or monochasial cymes or
thyrses; flowers subtended by paired bracteoles, bracts and/or
bracteoles inconspicuous or conspicuous, sometimes with
multiple whorls of bracts subtending the flowers; calyces vary-
ing from equally to highly unequally 5-lobed or reduced to 4
highly unequal lobes through fusion of the anterior pair of
lobes; corollas variable in size, shape and color, strongly bilabi-
ate to subactinomorphic, rugula absent, aestivation quincuncial
(i.e., lateral lobes outermost in bud); androecium either of 4 sta-
mens, then didynamous to strongly so, or of 2 stamens plus 2–3
staminodes, anthers in taxa with 2 stamens bithecous, anthers
in taxa with 4 stamens either all bithecous or with 2 pairs bithe-
cous and 2 pairs monothecous, thecae in bithecous stamens ±
equally inserted on filament, parallel or slightly sagittate, with
or more often without short basal appendages; stigma either
2-lobed or with only 1 lobe developing, this either linear or en-
larged and f lattened; capsule fusiform or conspicuously rostrate,
or sometimes stipitate, 2–4-seeded, retinacula present, without
fracturing placentae; seeds discoid to lenticular, surfaces often
covered in hygroscopic trichomes, these rarely sparse or absent;
pollen variable, frequent forms include (1) globose, 3-porate or
3-colporate with a coarsely reticulate exine, (2) prolate, 3-col-
porate with a finely reticulate exine, or (3) globose to subprolate
3-porate (to 6-porate), with a gemmate, verrucose or rugose
sculpturing of the exine.
Note. –The tribal name Russeggereae predates Barlerieae
by seven years and so has nomenclatural priority. Russeggereae
was described by Meisner to accommodate two genera des-
cribed by Endlicher, Russeggera (= Lepidagathis)and
Schwabea, the latter of which is an excluded name in the cur-
rent classification. This name has never been used since its first
description, whereas the name Barlerieae has been applied fre-
quently to this tribe as currently circumscribed (e.g., Mank-
telow & al., 2001; McDade & al., 2008; Champluvier &
Darbyshire, 2012; Darbyshire & al., 2019a,c; Comito & al., in
rev.), and a comparison of citations on Google Scholar reveals
124 references to Barlerieae but 0 references to Russeggereae.
There is no option under the Code (Turland & al., 2018) to con-
serve names between the ranks of family and genus, but under
Art. 56, rejection of a name at any rank can be proposed. The
current authors are therefore preparing a proposal to reject the
name Russeggereae, given that abandoning Barlerieae would
be a “disadvantageous nomenclatural change”(Art. 56.1). In
the meantime, we maintain Barlerieae over Russeggereae in the
current classification. A description of Barlerieae is provided
above to clarify the circumscription of this tribe.
Lankesteriinae I.Darbysh. & E.Tripp subtr. nov. –Type:
Lankesteria Lindl.
Perennial herbs or shrubs with cystoliths; leaves opposite;
inflorescences of dense terminal spikes or thyrses, often with
conspicuous imbricate bracts or the bracts linear in some spe-
cies, paired bracteoles linear and inconspicuous; corolla yel-
low, orange, or white, salverform, subactinomorphic or with
sinus between the two adaxial lobes at a wider angle than
the other lobe sinuses, with trifurcating traces to the lobes,
filament curtain absent, aestivation left-contort; androecium
of 2 stamens plus (typically) 2 staminodes, anthers bithecous,
thecae inserted equally on the filament and held at an equal
height; stigma capitate, the lobes oblique; capsule 2-seeded,
seeds with hygroscopic trichomes covering the surfaces, sur-
face with concentric rings of ridges, the trichomes attached
to (and hiding) these ridges (fide Manktelow & al., 2001);
pollen 3-porate, triangular in polar view with flattened aper-
tural faces, pores surrounded by a granular circular area, in-
terapertural areas otherwise reticulate.
Whitfieldiinae I.Darbysh. & E.Tripp, subtr. nov. –Type:
Whitfieldia Hook.
Perennial herbs or shrubs with cystoliths; leaves opposite;
inflorescences variously spiciform or racemoid thyrses, some-
times compounded into a panicle, or fasciculate, glomerulate
or shortly umbellate; individual flowers or floral units sub-
tended by paired bracts (or bracteoles), these often conspicu-
ous, clasping and sometimes partially connate at least in bud;
calyces equally to somewhat unequally 5-lobed; corolla rang-
ing from subactinomorphic to bilabiate, with traces trifurcating
in the lobes, filament curtain absent, aestivation left-contort
(also reported as ascending-cochlear but this not observed by
the current authors); androecium of 4 stamens (rarely reduced
to 2 stamens plus 2 staminodes in some flowers), with or with-
out an additional staminode, anthers bithecous, thecae inserted
equally on the filament and held at an equal height; stigma
capitate, the lobes symmetrical; capsule 2- to 4-seeded, seeds
(where known) with concentric rings of coarse scales at least
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towards margin, surfaces lacking trichomes; pollen lenticular,
2-pororate, with a pronounced marginal girdle (this typically
psilate), or rarely globose and pantoforate, areas around the
pores granular or micro-echinate.
Note. –If Ritonia Benoist proves to be a member of Whit-
fieldiinae, then the description of the androecium must be
modified to include 2 stamens plus 2 staminodes as a non-
aberrant trait.
Tetrameriinae T.F.Daniel, Kiel & McDade, subtr. nov. –
Type: Tetramerium Nees.
Perennial herbs or shrubs with cystoliths; leaves opposite;
inflorescences in 1- to many-flowered dichasia, these borne in
leaf axils or in axils of bracts along spikes, racemes, or thyrses,
which are sometimes branched into panicles, flowers sub-
tended by paired bracteoles, bracts and/or bracteoles incon-
spicuous or conspicuous; corollas variable in size, shape and
color, rugula absent; androecium of 2 stamens and no stami-
nodes (4 stamens in Chalarothyrsus), anthers bithecous (mono-
thecous in Clinacanthus), thecae of a pair equally or subequally
inserted on filament, parallel to sagittate, lacking basal append-
ages; stigma usually 2-lobed; capsule clavate, 2–4-seeded, reti-
nacula present and usually not separating from inner capsule
wall at maturity (separating slightly in Henrya and Tetrame-
rium); seeds distinct and expelled from capsule on dehiscence
(indistinct by fusion with retinacula and capsule wall, and not
expelled from capsule valves in Aphanosperma and Chalaro-
thyrsus); seeds compressed, surfaces and margin smooth or
variously ornamented, trichomes usually absent (hygroscopic
trichomes present in Henrya insularis); pollen usually 3-
colporate, 6-pseudocolpate (see Daniel & al., 2008 for rare
variants).
Graptophyllinae T.Anderson in J. Proc. Linn. Soc., Bot. 7: 17.
1863, emend. Kiel, McDade, I.Darbysh. & T.F.Daniel –
Type: Graptophyllum Nees.
Perennial (rarely annual) herbs or shrubs or small trees
with cystoliths; leaves opposite; inflorescences terminal to axil-
lary, form highly variable, inflorescences consisting of 1- to
many-flowered dichasia in leaf axils or in axils of bracts in
axillary and/or terminal spikes, racemes, or thyrses (or, when
branched, in panicles of these), flowers subtended by paired
bracteoles, bracts and/or bracteoles inconspicuous or con-
spicuous; corollas variable in size, shape and color, bilabiate
to only weakly zygomorphic, rugula absent; androecium either
of 4 stamens or of 2 stamens plus 2 staminodes, 2 pairs of sta-
mens (or pairs comprising 1 stamen plus 1 staminode) some-
times with filaments basally fused, anthers in taxa with 2
stamens either bithecous or monothecous, anthers in taxa with
4 stamens either all bithecous or with 1 pair bithecous and 1
pair monothecous, thecae of a pair subequally or unequally in-
serted on filament, parallel or slightly oblique, with or without
short basal appendages; stigma usually bilobed, but sometimes
subfunnelform (e.g., some Chileranthemum); capsule clavate,
(2–) 4-seeded, retinacula present and not separating from inner
capsule wall at maturity; seeds (where known) discoid to
lenticular, surfaces variously ornamented or smooth, tri-
chomes absent; pollen most frequently prolate and
3-colporate, 6-pseudocolpate but can be 4-colporate,
8-pseudocolpate or sometimes 4-por(or)ate and echinate (in
Isotheca and some Herpetacanthus).
Monotheciinae Lindau in Bot Jahrb. Syst. 18: 56. 1893,
emend. Kiel, I.Darbysh. & T.F.Daniel –Type: Monothe-
cium Hochst.
Perennial herbs, shrubs or small trees with cystoliths;
leaves opposite, isophyllous to strongly anisophyllous; inflo-
rescences varying from terminal to axillary or sometimes
ramiflorous or cauliflorous, inflorescence form highly vari-
able, ranging from open dichasia to spicate or paniculate
thyrses, to contracted few-branched dichasia or flowers soli-
tary, flowers subtended by paired bracteoles, bracts and/or
bracteoles inconspicuous or conspicuous; corollas variable
in size, shape and color, bilabiate, upper lip often hooded, ru-
gula absent, lower lip often with 2 raised ridges and a central
furrow running into the throat; androecium of 2 stamens and
no staminodes (except in Ptyssiglottis staminodifera where 2
staminodes present), anthers bithecous or (Monothecium
only) monothecous, thecae of a pair subequally or unequally
inserted on filament, parallel or slightly oblique, with or more
commonly without basal appendages; stigma 2-lobed; capsule
(where known) clavate, 4-seeded, retinacula present and not
separating from inner capsule wall at maturity; seeds (where
known) lenticular, surfaces variously ornamented, often tu-
berculate, trichomes absent; pollen most frequently prolate
and 3-colporate, 6-pseudocolpate but with variation up to 4-
or 5-colporate, 8- or 10-pseudocolpate, and also spheroidal
pantoporate.
Below, we validate names for two genera from Madagas-
car that have been applied in the literature and in various data-
bases for several decades now but were not validly published
at the time of original description. The status of these genera
within the classification of Acanthaceae remains to be further
researched. These validations thus serve to facilitate future dis-
cussion. Small diagnostic descriptions are provided to aid id-
entification of these two poorly known taxa; full descriptions
are available in the original publications (Benoist, 1962).
Dolichostachys Benoist, gen. nov. –Type: Dolichostachys
elongata Benoist, sp. nov.
Validating description in Bull. Soc. Bot. France 109:
133. 1962.
Resembling Populina Baill. and allied genera in Tetra-
meriinae but differing in the very short corolla tube 4.5 mm
long (fide Benoist, 1962), in the broad, elliptic upper lip of
the corolla with a rounded apex, and in the long, narrowly ellip-
tic leaves 11–15 cm long when mature.
Dolichostachys elongata Benoist, sp. nov. –Holotype: Mada-
gascar: Fénérive, fl. 1912, Perrier de la Bâthie 9448 (P
[P00089215]*).
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Validating description in Bull. Soc. Bot. France 109:
133. 1962.
Additional material seen. –Madagascar, R. Mananara, fl.
Aug. 1912, Perrier de la Bâthie 9445 (P [P00089214]*).
Notes. –When describing Dolichostachys elongata,Be-
noist (1962) cited the two specimens listed above but did not
designate a type specimen, thus the names of the genus and spe-
cies were not validly published under Art. 40 of the Code
(Turland & al., 2018). This is rectified here by selection of
a type specimen. As Benoist provided full descriptions for the
genus and species (in Latin), the names can continue to be at-
tributed to him but with priority from the present publication.
Dolichostachys remains unplaced within Justicieae.
The combination of an androecium comprising two stamens
with parallel thecae and (apparently) lacking staminodes, a
2-lipped corolla with the lower lip deeply divided into 3
lobes and lacking raised venation in the throat, and a slender
spiciform inflorescence suggests possible affinity to Tetrame-
riinae, but Isoglossinae cannot be ruled out. Benoist (1962)
described the pollen as spherical and smooth with three pores.
Triporate pollen is observed in some Isoglossinae, notably in
Brachystephanus (Champluvier & Darbyshire, 2009), but in
those cases the grains are still conspicuously “girdled”as in
other Isoglossinae. It is possible that Benoist misinterpreted
this pollen type.
Vavara Benoist, gen. nov. –Type: Vavara breviflora (Benoist)
Benoist ex I.Darbysh. & E.Tripp, comb. nov.
Validating description in Bull. Soc. Bot. France 109:
134. 1962.
Resembling Dicliptera Juss. in its corolla tube twisted
through ±180° resulting in a resupinate corolla limb and ster-
notribic flower but differing in the anther thecae of each sta-
men being widely separated by long extension of the anther
connective (versus thecae immediately superposed or slightly
overlapping).
Vavara breviflora (Benoist) Benoist ex I.Darbysh. & E.Tripp,
comb. nov. ≡Rhinacanthus breviflorus Benoist in Notul.
Syst. (Paris) 12: 140. 1946 –Lectotype (designated
here): Madagascar, bassin supérieur du Mandrare (Sud-
Est), col de Vavara, fl. 10 Nov 1928, Humbert 6532 (P
[P00089211]*; isolectotypes: BM [BM013867026]!, K
[K000378866]!, P [P00089210]*, TAN [TAN000434]*).
Additional material seen. –Madagascar, chaine du Vo-
hibory (a l’ouest d’Ivohibe), fl. 1 Nov 1924, Humbert 3071
(P [P00089213]*); Prov. de Farafangana, entre Vondrozo et
Ivohibe, fl. 18 Sep 1926, Decary 5373 (P [P00089212]*).
Notes. –Benoist (1946) described Rhinacanthus brevi-
florus basedonthreecollections(Decary 5373;Humbert 3071,
6532) of which he designated Humbert 6532 as the type. As
there are several specimens of this gathering, we designate
(above) one of those at P as lectotype. When Benoist (1962)
later described his new genus Va v a r a containing the single
species V. breviflora, he failed to record that it was based on
R. breviflorus despite citing the same three collections
(without any type designation on this occasion). Therefore,
Va v a r a was not validly published under Art. 41 of the Code
(Turland & al., 2018). This is rectified here by formalizing
the new combination.
Vavara breviflora closely resembles some species of Di-
cliptera, most notably in corolla morphology, but the unique
arrangement of the anthers with the two thecae widely sepa-
rated by 0.8–1 mm appears to be diagnostic. Benoist (1946)
recorded the corolla as being sulphur-yellow, which would
be an additional diagnostic character, as Dicliptera has co-
rollas that range from white to purple or red. However, on
Decary 5373, the flower color is recorded as “white, slightly
pink”. We therefore consider it likely that Benoist’s (1946) re-
cord of the flower color is erroneous. We are confident that
this genus belongs within Justicieae-Justiciinae but molecular
data are needed to reveal its position in relation to Dicliptera
and allied genera.
V. New synonymies and combinations (species)
Below we provide new combinations and synonymies in
support of the proposed classification. Numerous other ac-
tions (e.g., subsequent combinations at the species level) re-
main to be advanced, pending further study, for example the
many new combinations needed in the expanded concept of
Strobilanthes.
Asystasia Blume in Bijdr. Fl. Ned. Ind.: 796. 1826 –Type:
Asystasia intrusa (Forssk.) Blume (= A. gangetica (L.)
T.Anderson subsp. micrantha (Nees) Ensermu).
Salpinctium was separated from Asystasia by Edwards &
Getliffe Norris (1989) on the basis of having compressed bi-
colporate pollen and an elongate linear corolla tube. However,
Ensermu & al. (1992) noted that bicolporate pollen is also re-
corded in at least one species of Asystasia in Africa, and pollen
is quite variable in the genus. Whilst the corolla tube in Asys-
tasia is usually infundibuliform, the length and width of the
tube is variable and in A. vogeliana from West and Central
Africa it is long and slender. Salpinctium was not upheld by
Ensermu & Vollesen (in Darbyshire & al., 2015) and this
decision is followed here. Combinations in Asystasia are al-
ready available for two of the three species treated in Salpinc-
tium by Edwards & Getliffe Norris (1989); below we make the
new combination for the third species, which is endemic to
Eswatini.
Asystasia hirsuta (T.J.Edwards) I.Darbysh. & E.Tripp, comb.
nov. ≡Salpinctium hirsutum T.J.Edwards in S. African J.
Bot. 55: 9. 1989 –Holotype: Eswatini, 3 miles S of Stegi,
fl. 25 Nov 1958, Compton 28397 (PRE [PRE0130612-0]*).
Aphelandra R.Br. in Prodr.: 475. 1810 –Type: Aphelandra
cristata (Jacq.) R.Br. ex W.T.Aiton (= A. pulcherrima
(Jacq.) Kunth).
=Orophochilus Lindau in Bull. Herb. Boissier 5: 657. 1897,
syn. nov. –Type: Orophochilus stipulaceus Lindau.
40 Version of Record
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=Rhombochlamys Lindau in Bull. Herb. Boissier 5: 659.
1897, syn. nov. –Type: Rhombochlamys rosulata Lindau
(≡Aphelandra rosulata (Lindau) Wassh.).
=Encephalosphaera Lindau in Bull. Herb. Boissier, ser. 2, 4:
322. 1904, syn. nov. –Type: Encephalosphaera vitellina
Lindau.
Although not sampled phylogenetically in McDade & al.
(2005), the monospecific genus Orophochilus is allied to spiny
members of Aphelandra. As such, we provide the necessary
combination below.
The genus Rhombochlamys was shown by McDade & al.
(2005) to be nested within Aphelandra with strong bootstrap
support, even though placed phylogenetically by only a single
locus. Nonetheless, those data in combination with morpho-
logical attributes discussed in McDade & al. (2005) suggest
that Rhombochlamys belongs within Aphelandra, and we
provide the necessary combination below. Note that R. rosu-
lata Lindau was previously transferred into Aphelandra by
D. Wasshausen in 1996.
The genus Encephalosphaera was shown by McDade & al.
(2005) to be nested within Aphelandra with strong bootstrap
support. As such, we provide the necessary combinations for
all species here. Note that no new combination is needed for
Encephalosphaera puberula (Leonard) Wassh., as this was
first published under Aphelandra puberula Leonard.
The genus Xantheranthemum was previously included
within Aphelandra (Wasshausen, 1996), which we follow here.
Aphelandra elata (Lindau) McDade & E.Tripp, comb. nov. ≡
Rhombochlamys elata Lindau in Bull. Herb. Boissier 5:
661. 1897 –Holotype: Colombia, prov. Cauca, über La Vi-
trera bei Palmira, fl. 17 Jun 1883, Lehmann 2891 (B†,
photo at F [neg. no. 8723]*; isotype: G [G00226595]*).
Aphelandra lasiandra (Mildbr.) McDade & E.Tripp, comb.
nov. ≡Encephalosphaera lasiandra Mildbr. in Notizbl.
Bot. Gart. Berlin-Dahlem 11: 68. 1930 –Holotype: Brazil,
Rio Acre, Seringal Saraguassu, fl. Feb 1911, Ule 9810 (B†,
photo at F [neg. no. 8721]*; isotype: K [K000534546]!).
Aphelandra stipulacea (Lindau) McDade & E.Tripp, comb.
nov. ≡Orophochilus stipulaceus Lindau in Bull. Herb.
Boissier 5: 658. 1897 –Holotype: Peru, Peruviae orienta-
lis, prope Tarapoto, fl., 1855–1856, Spruce 4324 (B†,
photo at F [neg. no. 8720]*; isotypes: BR [000006951306]*,
C [C10005068]*, G [G00236408]*, GH [00094151,
00094152]*, K [K000202098, K000202099]!, NY
[00312235]*, P [P00719696]*).
Aphelandra vitellina (Lindau) McDade & E.Tripp, comb.
nov. ≡Encephalosphaera vitellina Lindau in Bull. Herb.
Boissier, ser. 2, 4: 323. 1904 –Holotype: Colombia,
Prov. Popayan, “prope Agua Clara in Andibus occiden-
talis”, fl. Jan 1899, Lehmann 9048 (B†, photo at F
[neg. no. 8722]*; isotypes: K [K000534568]!, NY
[00311968]!).
Mimulopsis Schweinf. in Verh. K. K. Zool.-Bot. Ges. Wien
18: 677. 1868 –Type: Mimulopsis solmsii Schweinf.
=Ionacanthus Benoist in Notul. Syst. (Paris) 9: 65. 1940, syn.
nov. –Type: Ionacanthus calcaratus Benoist.
The Malagasy monospecific genus Ionacanthus was syn-
onymized with Mellera by Tripp & al. (2013a) on the basis of
phylogenetic data derived from Sanger sequencing but was
later included within a RADseq dataset (Tripp & Darbyshire,
2020) where it was resolved within Mimulopsis (including
Epiclastopelma). This latter result better aligns with morpho-
logical features, as Ionacanthus shares with Mimulopsis the
unique arrangement of the anthers in which the outermost
theca of each of the longer pair of stamens has a conspicuous
curved appendage, while the other thecae have much shorter
appendages or lack appendages. Ionacanthus is therefore here
transferred to Mimulopsis.
Mimulopsis calcarata (Benoist) E.Tripp & I.Darbysh., comb.
nov. ≡Ionacanthus calcaratus Benoist in Notul. Syst.
(Paris) 9: 65. 1940 ≡Mellera calcarata (Benoist) E.Tripp
in Int. J. Pl. Sci. 174: 128. 2013 –Holotype: Madagascar,
massif du Tsaratanana et haute vallée du Sambirano (ré-
serve naturelle no. 4), fl. & fr. Nov–Dec 1937, Humbert
18317 (P [P00435417]*; isotypes: K [K000394123]!, P
[P00435418]*, TAN [TAN000225]*).
Stenandriopsis S.Moore in J. Bot. 44: 153. 1906 –Type: Ste-
nandriopsis thompsonii S.Moore.
=Achyrocalyx Benoist in Bull. Soc. Bot. France 76: 1036.
1930, syn. nov. –Type: Achyrocalyx decaryi Benoist.
Vollesen (1992) transferred OW species previously treated
within Stenandriopsis to Stenandrium, which had previously
been treated as a NW genus, citing a lack of morphological
evidence for their separation. However, the NW and OW clades
are clearly separated phylogenetically (McDade & al., 2005)
and so Stenandriopsis is resurrected here. Combinations are
available for all but two of the species of OW Stenandrium;
as such, the new combinations are made below.
McDade & al. (2005) sampled one of the three species of
Achyrocalyx in their phylogenetic analysis of Acanthoideae
and found it to be resolved within the Stenandriopsis clade, re-
lated to the two sampled species of Malagasy Stenandriopsis.
Achyrocalyx was separated from Stenandriopsis by Benoist
(1930) on the basis of having a bilabiate corolla versus corolla
with five subequal lobes. However, McDade & al. (2005) noted
that several species of Stenandriopsis have a zygomorphic
corolla and, further, that plants of Achyrocalyx share with
Malagasy Stenandriopsis the character of having leaves in
pseudowhorls, a trait that Vollesen (1992) used in placing
African and Malagasy species of Stenandriopsis into differ-
ent sections. Hence, Achyrocalyx is best placed in Stenan-
driopsis and the new combinations are made here.
Stenandriopsis decaryi (Benoist) T.F.Daniel, McDade & Kiel,
comb. nov. ≡Achyrocalyx decaryi Benoist in Bull. Soc.
Bot. France 76: 1037. 1930 –Holotype: Madagascar,
Version of Record 41
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district d’Ambovombe, Ampasimpolaka, fl. 10 Jun
1924, Decary 2819 (P n.v.; isotypes: P n.v.).
=Achyrocalyx vicinus Benoist in Notul. Syst. (Paris) 8: 153.
1939 –Holotype: Madagascar, environs de Tuléar, fl. 7
Aug 1928, Humbert & Swingle 5215 (P n.v.; isotypes: G
[G00008600]*, K [K000394662]!, LISC [LISC 011410]*,
US [00664183]*).
Stenandriopsis grandiflora (Vollesen) T.F.Daniel, McDade
& Kiel, comb. nov. ≡Stenandrium grandiflorum Volle-
sen in Kew Bull. 55: 967. 2000 –Holotype: Tanzania,
Southern Udzungwa Escarpment, Kihansi River Gorge,
fl. & fr. 22 Jun 1995, Lovett 5053 (K [K000394700]!; iso-
types: DSM n.v., NHT [NHT000000436]*).
Stenandriopsis gossypina (Benoist) T.F.Daniel, McDade &
Kiel, comb. nov. ≡Achyrocalyx gossypinus Benoist in
Notul. Syst. (Paris) 8: 154. 1939 –Holotype: Madagascar,
Manampetsa, fl. Apr 1933, Perrier de la Bâthie 19185 (P
[P00089282]*; isotype: P [P00089283]*).
Stenandriopsis pauciflora (Vollesen) T.F.Daniel, McDade &
Kiel, comb. nov. ≡Stenandrium pauciflorum Vollesen in
Kew Bull. 47: 201. 1992 –Holotype: Madagascar, le long
de la piste d’Ampanihy àAmpotaka, fl. Mar 1960, Kerau-
dren 902 (P [P00083699]*; isotypes: K [K000394697]!,
P [P00083700]*).
Stenandriopsis pungens (Benoist) T.F.Daniel, McDade & Kiel,
comb. nov. ≡Achyrocalyx pungens Benoist in Notul. Syst.
(Paris) 12: 11. 1945 –Holotype: Madagascar, plateau de
Miandraraha dans le bassin du Manombo, fl. May 1910,
Perrier de la Bâthie 9507 (P [P00089284]*; isotypes: P
[P00089285, P00089286]*).
Stenostephanus Nees in Martius, Fl. Bras. 9: 91. 1847 –Type:
Stenostephanus lobeliiformis Nees.
=Kalbreyeriella Lindau in Notizbl. Bot. Gart. Berlin-Dahlem 8:
143. 1922, syn. nov. –Type: K. rostellata Lindau.
Kalbreyeriella has been distinguished from morphologi-
cally similar genera (i.e., most NW Isoglossinae, which are
now included in Stenostephanus) by the combination of its spi-
cate inflorescences, rostrate corolla buds, relatively long and
narrow upper lip of the corolla, and triangular and apically
acute (minutely 3-lobed) lower lip of the corolla (e.g., Leonard,
1958; Wasshausen, 2013). However, based on morphological
similarities, species of Razisea and Kalbreyeriella have been
suggested as better placed in Stenostephanus (Daniel, 1999).
Phylogenetic results of Kiel & al. (2006) support the inclusion
of Kalbreyeriella in Stenostephanus.Stenostephanus can be
characterized by bilabiate, more or less tubular corollas lacking
a rugula, two stamens with monothecous anthers, these held
with the style adjacent to the upper lip of the corolla, stamino-
dia lacking, and capsular fruits with the retinacula remaining
attached to the fruit wall. These plants also share pollen that
is banded or “girdled”(i.e., “Gürtelpollen”sensu Lindau,
1895). More recently, McDade & al. (2019) subsumed a spe-
cies of Costa Rican Kalbreyeriella into Stenostephanus.
Stenostephanus cabrerae (Leonard) T.F.Daniel, McDade &
Kiel, comb. nov. ≡Kalbreyeriella cabrerae Leonard in
Contr. U. S. Natl. Herb. 31: 408. 1958 –Holotype: Co-
lombia, Putumayo, Mocoa and vicinity, fl. & fr. 16 Mar
1953, Schultes & Cabrera 19093 (US [00136986]*).
Stenostephanus gigas (Leonard) T.F.Daniel, McDade & Kiel,
comb. nov. ≡Kalbreyeriella gigas Leonard in Contr.
U. S. Natl. Herb. 31: 412. 1958 –Holotype: Colombia,
Putumayo, entre Achipayacoy Mocoa, fl. & fr. 25 Dec
1940, Cuatrecasas 11271 (US [00136987]*; isotypes:
COL [COL000004528]*, F [V0047452F = No. 1334109]*).
Stenostephanus rostellatus (Lindau) T.F.Daniel, McDade &
Kiel, comb. nov. ≡Kalbreyeriella rostellata Lindau in
Notizbl. Bot. Gart. Berlin-Dahlem 8: 143. 1922 –Holo-
type: Colombia, Dep. Antioquia, Plateado, fl. 31 Mar 1880,
Kalbreyer 1524 (B†, photo at F [neg. no. 8801]*;isotype:
K [K000529532]!).
■AUTHOR CONTRIBUTIONS
EAMT and ID conceptualized the project. EAMT, ID, and TFD
wrote the manuscript and keys. EAMT, ID, TFD, CAK, and LAM revised
the manuscript. —EAMT, https://orcid.org/0000-0001-9340-8723; ID,
https://orcid.org/0000-0002-5514-9561, i.darbyshire@kew.org; TFD,
https://orcid.org/0000-0002-4497-0506, tdaniel@calacademy.org; CAK,
https://orcid.org/0000-0002-6773-2519, carrie.kiel@cgu.edu; LAM, https://
orcid.org/0000-0001-6504-8775, lucinda.mcdade@cgu.edu
■ACKNOWLEDGEMENTS
We thank Kaj Vollesen of the Royal Botanic Gardens, Kew for
his numerous contributions to building and revising knowledge of
Acanthaceae, and for his many years of collaboration. We acknow-
ledge the extensive contributions of Mariette Manktelow to improving
our understanding of members of Whitfieldieae, Dieter Wasshausen
for his invaluable contributions to our knowledge of South American
Acanthaceae, John Wood for his contribution to Acanthaceae taxon-
omy both in Asia and South America, Dominique Champluvier and
Kevin Balkwill for their contributions to African Acanthaceae, and
Deng Yunfei for contributing new knowledge of Asian Acanthaceae,
particularly those within Andrographideae. We are grateful to John
McNeill and Rafaël Govaerts, who provided valuable conversation
on nomenclatural issues. We thank Kanokorn (Ko) Rueangsawang of
Ramkhamhaeng University, Bangkok for helpful advice on some of the
genera that occur in Thailand. We are grateful to Kyle Dexter for his ex-
tensive field contributions towards our understanding of members of
Ruellieae. We dedicate the present work to the memory of Dr. Ensermu
Kelbessa, who contributed a lifetime of work to build vast new knowl-
edge of African Acanthaceae. Erin Manzitto-Tripp, Lucinda McDade,
and Carrie Kiel acknowledge support from the following awards from
the U.S. National Science Foundation: 1354963 & 1754493 (Univ. of
Colorado), 1355138 & 1754845 (California Botanic Garden). Erin
Manzitto-Tripp additionally acknowledges the Fulbright Global Scholars
Fellow Program for a 2020–2021 fellowship in Brazil.
42 Version of Record
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Appendix 1. List of accepted genera and generic synonyms based on the present reclassification. Some of the synonyms included below are illegitimate or not
validly published but we include them here because they have been mentioned in relevant literature.
Key: (Ac), Acantheae; (An), Andrographideae; (Av), Avicennioideae; (B), Barlerieae; (J), Justicieae; (Nel), Nelsonioideae; (Neu), Neuracantheae; (P), Physa-
cantheae; (Ru), Ruellieae; (T), Thunbergioideae; (W), Whitfieldieae; (IS), Incertae sedis.
Bold italics refers to genera recognized in the present work; italics refers to genera treated as synonyms in the present work.
*change in generic status since Scotland & Vollesen (2000); ** not recorded by Scotland & Vollesen (2000).
Acanthodium Delile = Blepharis
**Acanthodus Raf. = Acanthus
Acanthopale C.B.Clarke (Ru)
Acanthopsis Harv. (Ac)
*Acanthostelma Bidgood & Brummitt = Crabbea
*Acanthura Lindau = Lepidagathis
Acanthus L. (Ac)
Acelica Rizzini = Justicia
*Achyrocalyx Benoist = Stenandriopsis
**Adatoda Raf. = Justicia
Adelaster Lindl. ex Veitch = Fittonia
**Adeloda Raf. = Justicia
Adenacanthus Nees = Strobilanthes
**Adenosma Nees = Hygrophila
Adenostachya Bremek. = Strobilanthes
Adhatoda Mill. = Justicia
*Aechmanthera Nees = Strobilanthes
**Aetheilema N.Br. = Phaulopsis
Afrofittonia Lindau (J)
Afromendoncia Gilg ex Lindau = Mendoncia
**Aldelaster K.Koch = Pseuderanthemum
**Alvarezia Pav. ex Nees = Ruellia
Amathea Raf. = Aphelandra
Ambongia Benoist (J)
Amphiestes S.Moore = Hypoestes
Amphiscopia Nees = Justicia
Ancalanthus Balf.f. = Angkalanthus
Ancistranthus Lindau (J)
Ancistrostylis T.Yamaz. = Staurogyne
Ancylacanthus Lindau = Ptyssiglottis
**Ancylogyne Nees = Sanchezia
Androcentrum Lem. = Bravaisia
Andrographis Wall. ex Nees (An)
Angkalanthus Balf.f. (J)
Anisacanthus Nees (J)
Anisosepalum E.Hossain (Nel)
*Anisostachya Nees (J) [treated by some author-
ities as = Justicia]
Anisotes Nees (J)
Anomacanthus R.D.Good (T)
*Anthacanthus Nees = Oplonia
**Antheilema Raf. = Phaulopsis
Antheliacanthus Ridl. = Pseuderanthemum
**Anthocometes Nees = Monothecium
*Apassalus Kobuski = Dyschoriste
Aphanandrium Lindau = Neriacanthus
Aphanosperma T.F.Daniel (J)
Aphelandra R.Br. (Ac)
*Aphelandrella Mildbr. = Aphelandra
**Aphelandros St.-Lag. = Aphelandra
Aphragmia Nees = Ruellia
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Appendix 1. Continued.
*Apolepsis Hassk. = Strobilanthes
**Aporuellia C.B.Clarke = Ruellia
Arrhostoxylum Mart. ex Nees = Ruellia
Ascotheca Heine (J)
Asteracantha Nees = Hygrophila
Asystasia Blume (J)
Asystasiella Lindau = Asystasia
**Athlianthus Endl. = Justicia
**Aubletia Neck. = Ruellia
Aulojusticia Lindau = Justicia
Averia Leonard = Tetramerium
**Avicennia L. (Av)
**Aymoreana Braz, T.F.Daniel & Kiel (Nel)
**Bahel Adans. = Hygrophila
**Baillonacanthus Kuntze = Henrya
Ballochia Balf.f. (J)
Baphicacanthus Bremek. = Strobilanthes
Barleria L. (B)
Barleriacanthus Oerst. = Barleria
Barlerianthus Oerst. = Barleria
Barleriola Oerst. (B)
**Barleriopsis Oerst. = Barleria
Barleriosiphon Oerst. = Barleria
Barlerites Oerst. = Barleria
**Barreliera J.F.Gmel. = Barleria
Belantheria Nees = Brillantaisia
Beloperone Nees = Justicia
**Beloperonides Oerst. = Justicia
*Benoicanthus Heine & A.Raynal = Ruellia
Bentia Rolfe = Justicia
Berginia Harv. ex Benth. & Hook.f. =
Holographis
**Birnbaumia Kostel. = Anisacanthus
*Blechum P.Browne = Ruellia
Blepharacanthus Nees ex Lindl. = Blepharis
Blepharis Juss. (Ac)
**Bontia L. = Avicennia
Borneacanthus Bremek. (B)
Boutonia DC. (B)
Brachystephanus Nees (J)
Bravaisia DC. (Ru)
Bremekampia Sreem. = Haplanthodes
Brillantaisia P.Beauv. (Ru)
Brochosiphon Nees = Dicliptera
Brunoniella Bremek. (Ru)
Buceragenia Greenm. = Pseuderanthemum
Butayea De Wild. = Sclerochiton
Buteraea Nees = Strobilanthes
Calacanthus T.Anderson ex Benth. (Ru)
**Calasias Raf. = Anisotes
**Caldenbachia Pohl ex Nees = Stenandrium
Calliaspidia Bremek. = Justicia
Calophanes D.Don = Dyschoriste
Calophanoides (C.B.Clarke) Ridl. = Justicia
Calycacanthus K.Schum. (J)
Calymmostachya Bremek. = Justicia
*Camarotea Scott-Elliot (W)
**Campylostemon E.Mey. = Justicia
Cardanthera Buch.-Ham. ex Benth. =
Hygrophila
Cardiacanthus Nees & Schauer = Carlowrightia
**Carima Raf. = Justicia
Carlowrightia A.Gray (J)
Carvia Bremek. = Strobilanthes
Celerina Benoist (J)
*Centrilla Lindau = Justicia
Cephalacanthus Lindau (J)
**Cephalophis Vollesen (J)
Chaetacanthus Nees = Dyschoriste
Chaetochlamys Lindau = Justicia
Chaetothylax Nees = Justicia
Chaetothylopsis Oerst. = Justicia
Chalarothyrsus Lindau (J)
Chamaeranthemum Nees (J)
Championella Bremek. = Strobilanthes
**Champluviera I.Darbysh., T.F.Daniel &
Kiel (J)
Cheilopsis Moq. = Acanthus
Chileranthemum Oerst. (J)
Chiloglossa Oerst. = Justicia
Chingiacanthus Hand.-Mazz. = Isoglossa
*Chlamydacanthus Lindau (W)
Chlamydocardia Lindau (J)
*Chlamydostachya Mildbr. = Anisotes
Chorisochora Vollesen (J)
Chrestienia Montrouz. ex Beauvis. =
Pseuderanthemum
Chroesthes Benoist (B)
**Citharella Noronha = Eranthemum
*Clarkeasia J.R.I.Wood = Strobilanthes
Clinacanthus Nees (J)
Clistax Mart. (J)
Codonacanthus Nees (J)
*Conocalyx Benoist = Isoglossa
Copioglossa Miers = Ruellia
**Corna Noronha = Avicennia
Corymbostachys Lindau = Anisostachya
**Corythacanthus Nees = Clistax
Cosmianthemum Bremek. (J)
Crabbea Harv. (B)
**Crateola Raf. = Oplonia
Croftia Small = Carlowrightia
Crossandra Salisb. (Ac)
Crossandrella C.B.Clarke (Ac)
Cryphiacanthus Nees = Ruellia
Cryptophragmium Nees = Gymnostachyum
Ctenopaepale Bremek. = Strobilanthes
**Cuenotia Rizzini = Aphelandra
Cyclacanthus S.Moore (J)
**Cylindrosolen Kuntze = Stenostephanus
*Cylindrosolenium Lindau = Stenostephanus
Cynarospermum Vollesen (Ac)
Cyphacanthus Leonard (Ac)
Cyphisia Rizzini = Justicia
**Cyrtacanthus Mart. ex Nees = Ruellia
Cyrtanthera Nees = Justicia
Cyrtantherella Oerst. = Justicia
*Cystacanthus T.Anderson = Phlogacanthus
Dactylostegium Nees = Dicliptera
Daedalacanthus T.Anderson = Eranthemum
*Danguya Benoist = Anisotes
Dasytropis Urb. (J)
Delphinacanthus Benoist = Pseudodicliptera
Dianthera L. = Justicia
**Diapedium J.Koenig = Dicliptera
Diateinacanthus Lindau = Odontonema
Dicentranthera T.Anderson = Asystasia
*Diceratotheca J.R.I.Wood & Scotland (Ru)
Dichazothece Lindau (J)
Dicladanthera F.Muell. (J)
Dicliptera Juss. (J)
Dicranacanthus Oerst. = Barleria
Didyplosandra Wight ex Bremek.
=Strobilanthes
Diflugossa Bremek. = Strobilanthes
**Digyroloma Turcz. = Justicia
**Dilicaria T.Anderson = Acanthus
**Dilivaria Juss. = Acanthus
Dimanisa Raf. = Justicia
*Dinteracanthus Schinz (Ru)
Diotacanthus Benth. (An)
**Diplanthera Gled. = Justicia
**Diplocalymma Spreng. = Thunbergia
**Diptanthera Schrank ex Steud. = Justicia
Dipteracanthus Nees = Ruellia
Dischistocalyx T.Anderson ex Benth. (Ru)
Disperma J.F.Gmel. = Duosperma
Distichocalyx Benth. = Dischistocalyx
Ditrichospermum Bremek. = Strobilanthes
**Dizygandra Meisn. = Ruellia
*Dolichostachys Benoist (J)
**Donatia Loefl. = Avicennia
Dossifluga Bremek. = Strobilanthes
*Drejera Nees = Thyrsacanthus
Drejerella Lindau = Justicia
**Drupina L. = Mendoncia
Duosperma Dayton (Ru)
Duvernoia E.Mey. ex Nees = Justicia
Dyschoriste Nees (Ru)
Dyspemptemorion Bremek. = Justicia
**Earlia F.Muell. = Graptophyllum
**Eberlea Riddell ex Nees = Hygrophila
Ebermaiera Nees = Staurogyne
**Ecbolium Kuntze = Justicia
Ecbolium Kurz (J)
Echinacanthus Nees (Ru)
Echinopaepale Bremek. = Strobilanthes
Ecteinanthus T.Anderson = Isoglossa
Elytraria Michx. (Nel)
Emularia Raf. = Justicia
*Encephalosphaera Lindau = Aphelandra
**Endomelas Raf. = Thunbergia
Endopogon Nees = Strobilanthes
Endosiphon T.Anderson ex Benth. = Ruellia
**Engelia H.Karst. ex Nees = Mendoncia
*Epiclastopelma Lindau = Mimulopsis
Eranthemum L. (Ru)
Eremomastax Lindau (Ru)
**Erianthera Nees = Andrographis
Eriostrobilus Bremek. = Strobilanthes
Erythracanthus Nees = Staurogyne
Ethesia Raf. = Justicia
Eurychanes Nees = Ruellia
*Eusiphon Benoist = Ruellia
**Fabria E.Mey. = Ruellia
Filetia Miq. (J)
Fittonia Coem. (J)
**Flavicoma Raf. = Schaueria
**Flemingia Roxb. ex Rottler = Thunbergia
*Forcipella Baill. (W)
Forsythiopsis Baker = Oplonia
Galeottia Nees = Stenostephanus
*Gantelbua Bremek. = Strobilanthes
Gastranthus Moritz ex Benth. & Hook.f.
=Stenostephanus
Gatesia A.Gray = Yeatesia
*Geissomeria Lindl. = Aphelandra
Gendarussa Nees = Justicia
Gerardia L. = Stenandrium
**Geunsia Neck. ex Raf. = Dicliptera
Gilletiella De Wild. & T.Durand
=Anomacanthus
Glockeria Nees = Stenostephanus
Glosarithys Rizzini = Justicia
Glossochilus Nees (J)
*Golaea Chiov. = Crabbea
Goldfussia Nees = Strobilanthes
Graphandra J.B.Imlay (An)
Graptophyllum Nees (J)
**Gromovia Regel = Justicia
Gutzlaffia Hance = Strobilanthes
Gymapsis Bremek. = Strobilanthes
**Gymnacanthus Nees = Ruellia
Gymnacanthus Oerst. = Ruellia
*Gymnophragma Lindau [excluded]
Gymnostachyum Nees (An)
48 Version of Record
Manzitto-Tripp & al. •Revised classification and keys to Acanthaceae TAXON 00 (00) •1–51

Appendix 1. Continued.
*Gynocraterium Bremek. = Staurogyne
Gypsacanthus E.J.Lott, V.Jaram. & Rzed. (J)
Habracanthus Nees = Stenostephanus
Haemacanthus S.Moore = Satanocrater
Hallieracantha Stapf = Ptyssiglottis
**Halodendron Roem. & Schult. = Avicennia
**Halodendrum Thouars = Avicennia
Hansteinia Oerst. = Stenostephanus
Haplanthera Hochst. = Ruttya
Haplanthodes Kuntze (An)
*Haplanthoides H.W.Li = Haplanthus
*Haplanthus Nees (An)
Harnieria Solms = Justicia
Harpochilus Nees (J)
Harrachia Jacq. = Crossandra
Haselhoffia Lindau = Physacanthus
Heinzelia Nees = Justicia
Hemiadelphis Nees = Hygrophila
Hemichoriste Nees = Justicia
**Hemidelphus Nees = Hygrophila
*Hemigraphis Nees (Ru) = Strobilanthes
Hemisandra Scheidw. = Aphelandra
**Hemitome Nees = Aphelandra
**Hemonacanthus Nees = Ruellia
Henrya Benth. (J)
*Herpetacanthus Nees (J)
**Hesperanthemum Kuntze = Oplonia
Heteradelphia Lindau (Ru)
Heteraspidia Rizzini = Justicia
**Hexacentris Nees = Thunbergia
**Hilairanthus Tiegh. = Avicennia
Himantochilus T.Anderson ex Benth. = Anisotes
Holographis Nees (Ac)
**Holtzendorffia Klotzsch & H.Karst. ex Nees
=Ruellia
**Homilacanthus S.Moore = Isoglossa
**Homotropium Nees = Dyschoriste
Hoverdenia Nees (J)
Hulemacanthus S.Moore (B)
Hydromestus Scheidw. = Aphelandra
Hygrophila R.Br. (Ru)
Hymenochlaena Bremek. = Strobilanthes
Hypoestes Sol. ex R.Br. (J)
Ichthyostoma Hedrén & Vollesen (J)
**Idanthisa Raf. = Anisacanthus
*Indoneesiella Sreem. = Andrographis
**Intrusaria Raf. = Asystasia
*Ionacanthus Benoist = Mimulopsis
Isacanthus Nees = Sclerochiton
Isaloa Humbert = Barleria
Isochoriste Miq. = Asystasia
Isoglossa Oerst. (J)
Isotheca Turrill (J)
Ixtlania M.E.Jones = Justicia
Jacobinia Nees ex Moric. = Justicia
Jadunia Lindau (J)
**Janasia Raf. = Phlogacanthus
**Jungia Boehm. = Justicia
*Juruasia Lindau = Herpetacanthus
Justicia L. (J)
Kalbreyeracanthus Wassh. = Stenostephanus
*Kalbreyeriella Lindau = Stenostephanus
Kanjarum Ramam. = Strobilanthes
**Kenyacanthus I.Darbysh. & Kiel (J)
Kita A.Chev. = Hygrophila
Kjellbergia Bremek. = Strobilanthes
Kolobochilus Lindau = Razisea
Kosmosiphon Lindau (Ru)
*Kudoacanthus Hook. (J)
Kuestera Regel = Justicia
**Kuniria Raf. = Dicliptera
Lagochilium Nees = Aphelandra
Lamiacanthus Kuntze = Strobilanthes
*Lankesteria Lindl. (W)
Larsenia Bremek. = Strobilanthes
**Larysacanthus Oerst. = Ruellia
*Lasiocladus Bojer ex Nees (B)
*Leandriella Benoist (W)
Leda C.B.Clarke = Isoglossa
Leiophaca Lindau = Whitfieldia
Lepidacanthus C.Presl = Aphelandra
Lepidagathis Willd. (B)
Leptacanthus Nees = Strobilanthes
Leptosiphonium F.Muell. (Ru)
**Leptostachya Nees (J)
Leucobarleria Lindau = Neuracanthus
Leucorhaphis Nees = Brillantaisia
*Liberatia Rizzini = Lepidagathis
Libonia K.Koch = Justicia
Linariantha B.L.Burtt & R.M.Sm. (J)
Lindauea Rendle = Lepidagathis
*Linocalix Lindau = Chlamydocardia
**Linostylis Fenzl ex Sond. = Dyschoriste
Lirayea Pierre = Mendoncia
Lissospermum Bremek. = Strobilanthes
Listrobanthes Bremek. = Strobilanthes
*Lophostachys Pohl = Lepidagathis
Lophothecium Rizzini = Justicia
Louteridium S.Watson (Ru)
**Loxanthus Nees = Phlogacanthus
Lundellia Leonard = Holographis
Lustrinia Raf. = Justicia
*Lychniothyrsus Lindau = Ruellia
Mackaya Harv. (J)
Mackenziea Nees = Strobilanthes
Macrorungia C.B.Clarke = Metarungia
Mananthes Bremek. = Justicia
**Marama Raf. = Graptophyllum
Marcania J.B.Imlay (J)
**Mcdadea E.Tripp & I.Darbysh. (Ru)
Megalochlamys Lindau (J)
*Megalostoma Leonard = Justicia
Megaskepasma Lindau (J)
**Meiosperma Raf. (J)
Melittacanthus S.Moore (J)
Mellera S.Moore (Ru)
Mendoncia Vell. ex Vand. (T)
**Mendozia Ruiz & Pav. = Mendoncia
**Meninia Fua ex Hook.f. = Phlogacanthus
Metarungia Baden (J)
Mexacanthus T.F.Daniel (J)
Meyenia Nees (T)
**Micraea Miers = Ruellia
Micranthus J.C.Wendl. = Phaulopsis
Microstrobilus Bremek. = Strobilanthes
Mimulopsis Schweinf. (Ru)
Mirandea Rzed. (J)
Monachochlamys Baker = Mendoncia
*Monechma Hochst. = Meiosperma
Monothecium Hochst. (J)
*Morsacanthus Rizzini = Pseuderanthemum
**Neesiella Sreem. = Andrographis
Nelsonia R.Br. (Nel)
Neohallia Hemsl. = Justicia
Neolindenia Baill. = Louteridium
**Neowedia Schrad. = Ruellia
Neozenkerina Mildbr. = Staurogyne
Neriacanthus Benth. (Ac)
*Neuracanthus Nees (Neu)
Nicoteba Lindau = Justicia
**Nigrolea Noronha = Staurogyne
Nilgirianthus Bremek. = Strobilanthes
Nomaphila Blume = Hygrophila
Nothoruellia Bremek. = Ruellia
Odontonema Nees (J)
Odontonemella Lindau = Mackaya
Odontophyllum Sreem. = Aphelandra
Odontostigma Zoll. & Moritzi
=Gymnostachyum
Onus Gilli = Mellera
Onychacanthus Nees = Bravaisia
*Ophiorrhiziphyllon Kurz = Staurogyne
*Ophthalmacanthus Nees = Ruellia
Oplonia Raf. (J)
*Oreacanthus Benth. = Brachystephanus
Oreothyrsus Lindau = Ptyssiglottis
*Orophochilus Lindau = Aphelandra
Orthotactus Nees = Justicia
**Oryzetes Salisb. = Hygrophila
Pachystachys Nees (J)
Pachystrobilus Bremek. = Strobilanthes
**Panemata Raf. = Dicliptera
Parabarleria Baill. = Barleria
Parachampionella Bremek. = Strobilanthes
Paragoldfussia Bremek. = Strobilanthes
Paragutzlaffia H.P.Tsui = Strobilanthes
*Parajusticia Benoist = Gymnostachyum
Pararuellia Bremek. & Nann.-Bremek. (Ru)
Parastrobilanthes Bremek. = Strobilanthes
Parasympagis Bremek. = Strobilanthes
Parasystasia Baill. = Asystasia
**Pattersonia J.F.Gmel. = Ruellia
Paulowilhelmia Hochst. = Eremomastax
*Pelecostemon Leonard = Justicia
Pentstemonacanthus Nees = Ruellia
*Perenideboles Ram.Goyena = Megaskepasma
Periblema DC. = Boutonia
*Pericalypta Benoist (B)
Periestes Baill. = Hypoestes
Perilepta Bremek. = Strobilanthes
*Peristrophe Nees = Dicliptera [maintained as
distinct by some authorities]
Petalanthera Raf. = Justicia
Petalidium Nees (Ru)
Petracanthus Nees = Gymnostachyum
Phaulopsis Willd. (Ru)
Phaylopsis Willd. = Phaulopsis
Phialacanthus Benth. (J)
Phidiasia Urb. = Odontonema
Phillipsia Rolfe = Dyschoriste
Phlebophyllum Nees = Strobilanthes
Phlogacanthus Nees (An)
**Phyllophiorhiza Kuntze = Staurogyne
Physacanthus Benth. (P)
**Physichilus Nees = Hygrophila
**Pigafetta Adans. = Eranthemum
Plaesianthera (C.B.Clarke) Livera = Hygrophila
Plagiacanthus Nees = Justicia
Plagiotheca Chiov. = Isoglossa
**Planetanthemum (Endl.) Kuntze
=Pseuderanthemum
Plegmatolemma Bremek. = Justicia
**Pleimeris Raf. = Thunbergia
Pleocaulus Bremek. = Strobilanthes
**Pleuremidis Raf. = Thunbergia
Pleuroblepharis Baill. = Crossandra
*Podorungia Baill. (B)
**Poecilocnemis Martius ex Nees = Aphelandra
*Pogonospermum Hochst. (J)
Poikilacanthus Lindau (J)
**Polyechma Hochst. = Hygrophila
*Polylychnis Bremek. = Ruellia
Polythrix Nees = Crossandra
Polytrema C.B.Clarke = Ptyssiglottis
Populina Baill. (J)
Porphyrocoma Scheidw. ex Hook. = Justicia
Version of Record 49
TAXON 00 (00) •1–51 Manzitto-Tripp & al. •Revised classification and keys to Acanthaceae

Appendix 1. Continued.
Pounguia Benoist = Whitfieldia
Pranceacanthus Wassh. (J)
Pringleophytum A.Gray = Holographis
Prionitis Oerst. = Barleria
Psacadocalymma Bremek. = Justicia
Psacadopaepale Bremek. = Strobilanthes
Pseudacanthopale Benoist = Strobilanthopsis
Pseudaechmanthera Bremek. = Strobilanthes
Pseuderanthemum Radlk. (J)
Pseudobarleria Oerst. = Barleria
Pseudobarleria T.Anderson = Petalidium
Pseudoblepharis Baill. = Sclerochiton
Pseudocalyx Radlk. (T)
*Pseudodicliptera Benoist (B)
*Pseudoruellia Benoist = Ruellia
Pseudostenosiphonium Lindau = Strobilanthes
Psilanthele Lindau (J)
*Psiloesthes Benoist = Dicliptera
Pteracanthus (Nees) Bremek. = Strobilanthes
Pteroptychia Bremek. = Strobilanthes
Ptyssiglottis T.Anderson (J)
Pulchranthus V.M.Baum, Reveal & Nowicke (J)
Pupilla Rizzini = Justicia
Pyrrothrix Bremek. = Strobilanthes
**Racka Bruce ex J.F.Gmel. = Avicennia
**Racua J.F.Gmel. = Avicennia
*Ramusia Nees = Isoglossa
*Razisea Oerst. = Stenostephanus
Rhacodiscus Lindau = Justicia
Rhaphidosperma G.Don = Justicia
Rhaphidospora Nees = Justicia
Rhinacanthus Nees (J)
*Rhombochlamys Lindau = Aphelandra
Rhyticalymma Bremek. = Justicia
Rhytiglossa Nees ex Lindl. = Isoglossa
*Ritonia Benoist (IS)
Rodatia Raf. = Justicia
**Roslinia Neck. = Justicia
Rostellaria Nees = Justicia
Rostellularia Rchb. = Justicia
Ruellia L. (Ru)
Ruelliola Baill. = Brillantaisia
Ruelliopsis C.B.Clarke (Ru)
Rungia Nees (J) [treated by some authorities
as = Justicia]
Ruspolia Lindau (J)
**Russeggera Endl. = Lepidagathis
Ruttya Harv. (J)
Saglorithys Rizzini = Justicia
Saintpauliopsis Staner (Nel)
Salpinctium T.J.Edwards = Asystasia
Salpingacanthus S.Moore = Ruellia
Salpingantha Lem. = Salpixantha
Salpinxantha Urb. = Salpixantha
Salpixantha Hook. (Ac)
Salviacanthus Lindau = Justicia
Samuelssonia Urb. & Ekman (J)
Sanchezia Ruiz & Pav. (Ru)
Santapaua N.P.Balakr. & Subram. = Hygrophila
Sapphoa Urb. (J)
**Sarcanthera Raf. = Gymnostachyum
Sarojusticia Bremek. = Justicia
Sarotheca Nees = Justicia
Satanocrater Schweinf. (Ru)
*Sautiera Decne. = Dyschoriste
**Sceura Forssk. = Avicennia
Schaueria Nees (J)
**Schaueriopsis Champl. & I.Darbysh. (B)
Schliebenia Mildbr. = Isoglossa
**Schmidia Wight = Thunbergia
**Schultzia Nees = Herpetacanthus
Schwabea Endl. [excluded]
Sciaphyllum Bremek. = Pachystachys
Sclerocalyx Nees = Ruellia
Sclerochiton Harv. (Ac)
**Scorodoxylum =Ruellia
Sebastiano-Schaueria Nees (J)
**Sebschauera Kuntze = Sebastiano-Schaueria
Semnostachya Bremek. = Strobilanthes
Semnothyrsus Bremek. = Strobilanthes
**Senkebergia Neck. ex Raf. = Mendoncia
**×Sericobonia Linden & André = Justicia
Sericocalyx Bremek. = Strobilanthes
Sericographis Nees = Justicia
**Sericospora Nees [excluded]
Simonisia Nees = Justicia
Sinthroblastes Bremek. = Strobilanthes
Siphonacanthus Nees = Ruellia
**Siphoneranthemum (Oerst.) Kuntze
=Pseuderanthemum
Siphonoglossa Oerst. = Justicia
**Solaenacanthus Oerst. = Ruellia
*Solenochasma Fenzl = Dicliptera
Solenoruellia Baill. = Henrya
**Somalia Oliv. = Barleria
*Sooia Pócs = Mimulopsis
**Soubeyrania Neck. = Barleria
Spathacanthus Baill. (J)
*Sphacanthus Benoist (J)
*Sphinctacanthus Benth. (An)
*Spirostigma Nees = Ruellia
Sreemadhavana Rauschert = Aphelandra
**Stachyacanthus Nees = Ruellia
Standleyacanthus Leonard = Herpetacanthus
Staurogyne Wall. (Nel)
Staurogynopsis Mangenot & Aké Assi
=Staurogyne
Steirosanchezia Lindau = Sanchezia
Stemonacanthus Nees = Ruellia
*Stenandriopsis S.Moore (Ac) [treated by some
authorities as = Stenandrium]
Stenandrium Nees (Ac)
Stenoschista Bremek. = Ruellia
*Stenosiphonium Nees = Strobilanthes
Stenostephanus Nees (J)
Stenothyrsus C.B.Clarke (Ru)
Stephanophysum Pohl = Ruellia
Stethoma Raf. = Justicia
**Stiftia Pohl ex Nees = Staurogyne
Streblacanthus Kuntze (J)
**Strepsiphus Raf. = Dicliptera
Streptosiphon Mildbr. (Ac)
*Strobilacanthus Griseb. [excluded, possibly
=Crossandra]
Strobilanthes Blume (Ru)
Strobilanthopsis S.Moore (Ru)
Strobilorhachis Klotzsch = Aphelandra
Strophacanthus Lindau = Isoglossa
Styasasia S.Moore = Asystasia
Stylarthropus Baill. = Whitfieldia
Suessenguthia Merxm. (Ru)
Supushpa Suryan. = Strobilanthes
Sympagis (Nees) Bremek. = Strobilanthes
Symplectochilus Lindau = Anisotes
Synandra Schrad. = Aphelandra
Synchoriste Baill. = Lasiocladus
Synnema Benth. = Hygrophila
Syringidium Lindau = Stenostephanus
Tabascina Baill. = Justicia
Tacoanthus Baill. = Ruellia
Taeniandra Bremek. = Strobilanthes
Talbotia S.Moore = Afrofittonia
Tarphochlamys Bremek. = Strobilanthes
Teliostachya Nees = Lepidagathis
**Tenoria Dehnh & Giord. = Hygrophila
Tessmanniacanthus Mildbr. (J)
Tetraglochidium Bremek. = Strobilanthes
Tetragoga Bremek. = Strobilanthes
Tetragompha Bremek. = Strobilanthes
Tetramerium Nees (J)
Thalestris Rizzini = Justicia
Thamnojusticia Mildbr. = Justicia
*Theileamea Baill. = Phaulopsis
Thelepaepale Bremek. = Strobilanthes
Thunbergia Retz. (T)
*Thyrsacanthus Moric. (J)
Thyrsacanthus Nees = Odontonema
Thysanostigma J.B.Imlay (J)
Tremacanthus S.Moore = Ruellia
Triaenacanthus Nees = Strobilanthes
Trichacanthus Zoll. & Moritzi = Blepharis
Trichanthera Kunth (Ru)
Trichaulax Vollesen (J)
Trichocalyx Balf.f. (J)
Trichosanchezia Mildbr. (Ru)
**Trixanthera Raf. = Trichanthera
Trybliocalyx Lindau = Chileranthemum
Tubiflora J.F.Gmel. = Elytraria
Tyloglossa Hochst. = Justicia
Ulleria Bremek. = Ruellia
**Upata Adans. = Avicennia
**Upudalia Raf. = Eranthemum
**Vada-kodi Adans. = Justicia
**Valentiana Raf. = Thunbergia
*Vavara Benoist (J)
*Vindasia Benoist (W)
Volkensiophyton Lindau = Lepidagathis
Warpuria Stapf = Podorungia
*Whitfieldia Hook. (W)
**Wuacanthus Y.F.Deng, N.H.Xia & H.Peng (J)
*Xantheranthemum Lindau = Aphelandra
Xanthostachya Bremek. = Strobilanthes
Xenacanthus Bremek. = Strobilanthes
Xerothamnella C.T.White (J)
**Xylacanthus Aver. & K.S.Nguyen (Ru)
Yeatesia Small (J)
**Zahlbrucknera Pohl ex Nees = Lepidagathis
Zenkerina Engl. = Staurogyne
**Zonablepharis Raf. = Acanthus
*Zygoruellia Baill. (W)
50 Version of Record
Manzitto-Tripp & al. •Revised classification and keys to Acanthaceae TAXON 00 (00) •1–51

Appendix 2. A proposed linear sequence for the currently accepted genera of Acanthaceae for use in systematically arranged natural history collections.
1Nelsonia R.Br.
2Elytraria Michx.
3Aymoreana Braz, T.F.Daniel & Kiel
4Anisosepalum E.Hossain
5Saintpauliopsis Staner
6Staurogyne Wall.
7Avicennia L.
8Mendoncia Vell. ex Vand.
9Anomacanthus R.D.Good
10 Pseudocalyx Radlk.
11 Thunbergia Retz.
12 Meyenia Nees
13 Crossandra Salisb.
14 Crossandrella C.B.Clarke
15 Streptosiphon Mildbr.
16 Sclerochiton Harv.
17 Cynarospermum Vollesen
18 Blepharis Juss.
19 Acanthopsis Harv.
20 Acanthus L.
21 Stenandriopsis S.Moore
22 Stenandrium Nees
23 Salpixantha Hook.
24 Neriacanthus Benth.
25 Holographis Nees
26 Aphelandra R.Br.
27 Cyphacanthus Leonard
28 Physacanthus Benth.
29 Neuracanthus Nees
30 Barleria L.
31 Crabbea Harv.
32 Lasiocladus Bojer ex Nees
33 Pericalypta Benoist
34 Podorungia Baill.
35 Pseudodicliptera Benoist
36 Boutonia DC.
37 Lepidagathis Willd.
38 Schaueriopsis Champl. & I.Darbysh.
39 Chroesthes Benoist
40 Hulemacanthus S.Moore
41 Borneacanthus Bremek.
42 Barleriola Oerst.
43 Andrographis Wall. ex Nees
44 Haplanthus Nees
45 Haplanthodes Kuntze
46 Graphandra J.B.Imlay
47 Phlogacanthus Nees
48 Gymnostachyum Nees
49 Diotacanthus Benth.
50 Sphinctacanthus Benth.
51 Lankesteria Lindl.
52 Whitfieldia Hook.
53 Chlamydacanthus Lindau
54 Zygoruellia Baill.
55 Camarotea Scott Elliot
56 Forcipella Baill.
57 Vindasia Benoist
58 Leandriella Benoist
59 Brunoniella Bremek.
60 Leptosiphonium F.Muell.
61 Pararuellia Bremek. & Nann.-Bremek.
62 Eranthemum L.
63 Kosmosiphon Lindau
64 Dinteracanthus Schinz
65 Dischistocalyx T.Anderson ex Benth.
66 Satanocrater Schweinf.
67 Acanthopale C.B.Clarke
68 Ruellia L.
69 Calacanthus T.Anders. ex Benth.
70 Louteridium S.Watson
71 Bravaisia DC.
72 Trichanthera Kunth
73 Trichosanchezia Mildbr.
74 Sanchezia Ruiz & Pav.
75 Suessenguthia Merxm.
76 Strobilanthes Blume
77 Hygrophila R.Br.
78 Brillantaisia P.Beauv.
79 Strobilanthopsis S.Moore
80 Dyschoriste Nees
81 Echinacanthus Nees
82 Petalidium Nees
83 Duosperma Dayton
84 Ruelliopsis C.B.Clarke
85 Mcdadea E.Tripp & I.Darbysh.
86 Phaulopsis Willd.
87 Eremomastax Lindau
88 Heteradelphia Lindau
89 Mellera S.Moore
90 Mimulopsis Schweinf.
91 Stenothyrsus C.B.Clarke
92 Xylacanthus Aver. & K.S.Nguyen
93 Diceratotheca J.R.I.Wood & Scotland
94 Spathacanthus Baill.
95 Chamaeranthemum Nees
96 Pranceacanthus Wassh.
97 Herpetacanthus Nees
98 Isotheca Turrill
99 Afrofittonia Lindau
100 Thysanostigma J.B.Imlay
101 Glossochilus Nees
102 Asystasia Blume
103 Phialacanthus Benth.
104 Filetia Miq.
105 Mackaya Harv.
106 Cosmianthemum Bremek.
107 Codonacanthus Nees
108 Chileranthemum Oerst.
109 Pulchranthus V.M.Baum, Reveal & Nowicke
110 Odontonema Nees
111 Sapphoa Urb.
112 Oplonia Raf.
113 Psilanthele Lindau
114 Linariantha B.L.Burtt & R.M.Sm.
115 Pseuderanthemum Radlk.
116 Graptophyllum Nees
117 Wuacanthus Y.F.Deng, N.H.Xia & H.Peng
118 Ruspolia Lindau
119 Ballochia Balf.f.
120 Ruttya Harv.
121 Champluviera I.Darbysh., T.F.Daniel & Kiel
122 Monothecium Hochst.
123 Marcania J. B.Imlay
124 Jadunia Lindau
125 Calycacanthus K.Schum.
126 Cyclacanthus S.Moore
127 Ptyssiglottis T.Anderson
128 Ambongia Benoist
129 Ichthyostoma Hedrén & Vollesen
130 Isoglossa Oerst.
131 Sphacanthus Benoist
132 Celerina Benoist
133 Melittacanthus S.Moore
134 Brachystephanus Nees
135 Stenostephanus Nees
136 Sebastiano-Schaueria Nees
137 Chlamydocardia Lindau
138 Leptostachya Nees
139 Kudoacanthus Hook.
140 Clinacanthus Nees
141 Angkalanthus Balf.f.
142 Chorisochora Vollesen
143 Ecbolium Kurz
144 Populina Baill.
145 Megalochlamys Lindau
146 Trichaulax Vollesen
147 Cephalophis Vollesen
148 Mirandea Rzed.
149 Yeatesia Small
150 Hoverdenia Nees
151 Thyrsacanthus Moric.
152 Pachystachys Nees
153 Fittonia Coem.
154 Schaueria Nees
155 Ancistranthus Lindau
156 Aphanosperma T.F.Daniel
157 Chalarothyrsus Lindau
158 Henrya Benth.
159 Gypsacanthus E.J.Lott, V.Jaram. & Rzed.
160 Carlowrightia A.Gray
161 Tetramerium Nees
162 Anisacanthus Nees
163 Mexacanthus T.F.Daniel
164 Streblacanthus Kuntze
165 Dolichostachys Benoist
166 Justicia L.
167 Ascotheca Heine
168 Rungia Nees
169 Metarungia Baden
170 Anisotes Nees
171 Anisostachya Nees
172 Trichocalyx Balf.f.
173 Meiosperma Raf.
174 Pogonospermum Hochst.
175 Kenyacanthus I.Darbysh. & Kiel
176 Rhinacanthus Nees
177 Hypoestes Sol. ex R.Br.
178 Dicliptera Juss.
179 Vavara Benoist
180 Xerothamnella C.T.White
181 Dicladanthera F.Muell.
182 Cephalacanthus Lindau
183 Poikilacanthus Lindau
184 Megaskepasma Lindau
185 Clistax Mart.
186 Harpochilus Nees
187 Dasytropis Urb.
188 Samuelssonia Urb. & Ekman
189 Dichazothece Lindau
190 Tessmanniacanthus Mildbr.
191 Ritonia Benoist
Version of Record 51
TAXON 00 (00) •1–51 Manzitto-Tripp & al. •Revised classification and keys to Acanthaceae